What is sexsomnia? And how can it be used as a defence in court?

This article first appeared in The Conversation here. The version below includes minor additions, as well as footnotes so that references to academic texts are clearer.

Related media: A follow-up interview with the author about sexsomnia and the criminal law may be heard on ABC Radio National’s The Law Report with Damien Carrick here. An article on SBS News: Life featuring quotations from the author may be read here. An article in WHO Magazine featuring quotations from the author may be viewed here.

Over the past decade, ‘sexsomnia’ has been used as a defence in a number of Australian sexual assault trials.¹ This sleep disorder — sometimes known as ‘sleep sex’ — causes people to engage in sexual behaviour while asleep.²

Last week, a Sydney man with sexsomnia was acquitted of rape charges.³ The dispute was not whether he had sex with the woman, nor whether she consented. The question was whether the man’s actions were voluntary. This turned on whether he was asleep or awake when he performed the acts.

The apparent increase in the use of the sexsomnia defence has raised concerns, both in Australia and overseas.⁴ Some claim the defence may be a way for people accused of sex crimes to evade justice.

In this latest case, the trial judge explained a well-established rule of criminal law to the jury. The rule is that a person cannot be held criminally responsible for involuntary acts.⁵ After deliberating, the jury found the man not guilty.

But how can sexsomnia be proved in court? Here’s what we know about this rare condition, and how it is used as a criminal defence.

What is sexsomnia?

Sexsomnia is not the same as having sex dreams. It is a parasomnia, or sleep disorder.⁶ It can cause the person to engage in sexual behaviour while unconscious, including sexual touching, intercourse or masturbation. Sexsomnia was only added to the Diagnostic Statistical Manual of Mental Disorders (DSM-5) in 2013.⁷ It sits alongside sleepwalking and night terrors.

People may not be aware they have sexsomnia. There are some potential triggers, including alcohol and stress.⁸ But there are also effective treatments, including the drug clonazepam, which has sedative effects, as well as some antidepressants.⁹

It’s unclear how common sexsomnia is, but it’s thought to be rare.¹⁰ A 2020 study found only 116 clinical cases had been recorded in the medical literature.¹¹ But it may also be underreported due to embarrassment and a lack of awareness.¹²

How is it used in court?

Sexsomnia is a recent version of an older legal defence known as automatism, which can be traced to the 1840s.¹³ Automatism describes actions without conscious volition (meaning without using your will).¹⁴ Those with automatism have no memory or knowledge of their acts.

The law has recognised automatism in sleep walking, in reflexes, spasms, or convulsions, and in acts of those with hypoglycaemia (low blood sugar) and epilepsy.¹⁵ But an important debate in the legal cases, as well as among psychiatrists and sleep experts, is about how to classify the condition.¹⁶

Essentially, is sexsomnia a mental health impairment caused by an underlying mental illness?¹⁷ Or is it a temporary “malfunction” that occurs in an otherwise “healthy mind”? Australian law has recognised sexsomnia as the latter (a kind of “sane automatism”) meaning it is characterised by episodes that don’t necessarily recur.¹⁸

How can sexsomnia be proved?

Detailed medical evidence is usually required for this defence. However, the defendant only needs to prove there was a “reasonable possibility” their acts were involuntary.¹⁹

By contrast, the prosecution must prove “beyond a reasonable doubt” that the sexual acts were voluntary or “willed” — a higher standard of proof.²⁰ This means it can be challenging to rule out sexsomnia once the defendant has presented evidence of the condition.

Is sexsomnia a mental illness?

Some important Australian cases²¹ have considered whether the law should treat sexsomnia as an ongoing mental disorder instead of a transitory “malfunction of the mind”.²²

In a 2022 case, prosecutors accepted that a New South Wales man accused of sexual offences against his daughter had sexsomnia.²³ What they contested was that his condition arose from a ‘sound mind.’ They argued sexsomnia should now be considered a mental illness. This argument capitalised on new laws that had commenced that year in NSW.²⁴ In defining mental health impairments, the new laws included a disturbance of volition.²⁵

Why is this significant?

The 2022 case was understood to have legal implications — not only for NSW but for all state jurisdictions in Australia.²⁶

If the prosecution could establish sexsomnia was a mental health impairment, then an outright acquittal would be unlikely. The prosecution would seek that the jury or judge return a special verdict of ‘act proven but not criminally responsible’ if satisfied that the defence of mental health impairment had been established.²⁷

Instead, the court might be required to reach a ‘special verdict’ and then to refer the defendant to a mental health tribunal.²⁸ As a result, the defendant could be detained in a secure psychiatric facility, such as the Long Bay Hospital.²⁹

However, the prosecution in the 2022 case failed to establish sexsomnia was the result of a mental health impairment under the new laws.³⁰ A two-judge majority said sexsomnia was not a ‘disturbance of volition’ because no one has volition when they are asleep. More specifically, Brereton JA, who wrote the leading judgment, said as follows:

he circumstance that a person does not have volition when asleep cannot be said to be a disturbance of an ordinary condition; it is an ordinary condition. It involves no diminution, deterioration or damage of ordinary functioning; it is ordinary functioning. There is no disturbance of volition.’³¹

The dissenting judge, Wilson JA, found that sexsomnia was a mental health impairment under the new definition. Her reasons highlighted that one purpose of the new laws was to ‘protect the safety of members of the public.’ Although her Honour dissented, Wilson JA’s conclusion is worth quoting at length to illustrate the basis of her alternative construction of the relevant provision, section 4, of the Mental Health and Forensic Provisions Act 2020 (NSW):

On my reading of the MHCIFP Act, its object was not to simply translate the common law into statute; it was to codify and modernise the law that relates to persons with a mental health or cognitive impairment, taking ‘into account the safety and experiences of victims, as well as [to] prioritise the safety of the community.’ So much is plain from the text of the legislation, even setting aside what was said by the Attorney in the second reading speech (at 2349) on 3 June 2020.

The principle of legality cannot, in my opinion, be relied upon to read the MHCIFP Act as no more than the codification of the common law. The legislation is broader than that. I am persuaded that there was error in the conclusions of the trial judge that led to him construing the meaning of s 4(1)(a) and (b) consistent with the common law concepts of a defect of reason caused by a disease of the mind, rather than in accordance with the plain meaning of the words, consistent with the purpose of the statute.

His Honour was not asked to, and did not, consider s 4(1)(c). If a textual and purposive construction is applied to s 4(1), the evidence establishes that, on the two occasions when he sexually touched his nine-year-old daughter, the respondent had a temporary disturbance of volition (s 4(1)(a)); his condition was regarded as clinically significant in that it met the diagnostic criteria for the disorder of sexsomnia (s 4(1)(b)); and the disturbance impaired his behaviour (s 4(1)(c)).³²

Why are these definitions controversial?

As long ago as 1966, legal scholars criticised how the law treats different kinds of automatism.³³ While sleepwalkers and sexsomniacs are viewed as ‘perfectly harmless,’ those with other conditions, such as schizophrenia, are viewed as “criminally demented” and detained in facilities under law.³⁴

Whether sexsomnia is a sleep disorder with non-recurring episodes or a more permanent mental disorder continues to be debated.³⁵ The title of Colleen Davis’s 2015 article tersely captures the controversy: ‘Sexsomnia — Excusable or Just Insane?’³⁶

However, the way sexsomnia is addressed clinically may reinforce its status as a sleep disorder. As there are no formal practice guidelines for treatments, it has tended to be sleep clinics, rather than psychiatrists, who respond to the condition.³⁷ Nevertheless, recent studies have indicated that sexsomnia has a pathophysicological basis: specifically, that it originates from a central pattern generator ‘in the brainstem and spinal cord, as opposed to the cerebral cortex.’³⁸

The increasing use of this rare condition as a defence in serious, violent cases of sexual assault is concerning and warrants further research and attention.

Where to from here?

This is a complex area of law with a complicated history of medico-legal jurisprudence. But in view of the warranted concerns about the increasing use of the sexsomnia defence in serious, violent cases of sexual transgressions, it may be appropriate to consider the reform proposal advanced by esteemed mental health law scholar Bernadette McSherry no less than twenty years ago.³⁹

That proposal considered various legislative reforms, including one that would limit the scope and legal definition of automatism. Although it may be difficult to draft, such a reform might, as McSherry suggested, prompt courts to draw sensible distinctions between different types of conduct.

The effect of this intervention could be that courts would be prompted to demand more or different evidence from those defendants whose charges involve complex ‘goal-directed’ or ‘purposive’ acts but who yet contend those acts were involuntary.

Given that the defence appears to be difficult to disprove, a reform of this description might ensure that those cases whose facts were deserving of more scrutiny were able to be scrutinised appropriately.

Notes

1. Harriet Alexander, ‘More sex offenders claiming “sexsomnia”‘ Sydney Morning Herald (online, 8 October 2014) https://www.smh.com.au/national/nsw/more-sex-offenders-claiming-sexsomnia-20141007-10rg8p.html; Heath Parkes-Hupton, ‘Man Acquitted of Daughter’s Sexual Abuse because he Experienced ‘Sexsomnia’ in his Sleep’, ABC News (online, 5 May 2022) https://www.smh.com.au/national/nsw/more-sex-offenders-claiming-sexsomnia-20141007-10rg8p.html. ↩︎
2. ‘What is Sleep Sex?’, Healthline (online, 7 June 2017) https://www.healthline.com/health/sleep-sex#symptoms ↩︎
3. Australian Associated Press, ‘Man with “Sexsomnia” not Guilty of Raping Woman after Judge warns Jury in Sydney Trial’, Guardian (online 30 January 2025) https://www.theguardian.com/australia-news/2025/jan/30/timothy-malcolm-rowland-sexsomnia-not-guilty-rape-sydney-ntwnfb. ↩︎
4. Parkes-Hupton, (n 1); ‘Spotlight on Sexsomnia Defence’, Law Times (online, 18 February 2008) https://www.lawtimesnews.com/news/general/spotlight-on-sexsomnia-defence/259440. ↩︎
5. Woolmington v DPP (1935) AC 462, 482; Colin Howard, ‘Automatism and Insanity’ (1962) Sydney Law Review 37 n 2 https://classic.austlii.edu.au/au/journals/SydLawRw/1962/3.pdf ↩︎
6. Andrea Cecilia Toscanini et al, ‘Sexsomnia: Case Based Classification and Discussion of Psychosocial Implications’ (2021) 14(2) Sleep Science (Sao Paulo, Brazil) 175 https://pmc.ncbi.nlm.nih.gov/articles/PMC8340885/. ↩︎
7. John A Fleetham and Jonathan AE Fleming, ‘Parasomnias’ (2014) 186(8) Canadian Medical Association Journal E273 https://pmc.ncbi.nlm.nih.gov/articles/PMC4016090/. ↩︎
8. ‘What is Sleep Sex?’ (n 2). ↩︎
9. Vineeth Kumar, Vincent X Grbach and Richard J Castriotta, ‘Resolution of Sexsomnia with Paroxetine’ (2020) 16(7) Journal of Clinical Sleep Medicine: 1213 https://pubmed.ncbi.nlm.nih.gov/32672534/. ↩︎
10. Alexandria Organ and J Paul Fedoroff, ‘Sexsomnia: Sleep Sex Research and Its Legal Implications’ (2015) 17(5) Current Psychiatry Reports 34 http://link.springer.com/10.1007/s11920-015-0568-y. ↩︎
11. Kumar, Grbach and Castriotta (n 9). ↩︎
12. Organ and Fedoroff (n 10). ↩︎
13. Ibid. ↩︎
14. CR Williams, ‘Development and Change in Insanity and Related Defences’ (2000) 24(3) Melbourne University Law Review 711 https://classic.austlii.edu.au/au/journals/MelbULawRw/2000/28.html ↩︎
15. Stanley Yeo, ‘Putting Voluntariness back into Automatism’ (2001) 32(2) Victoria University of Wellington Law Review 387 https://ojs.victoria.ac.nz/vuwlr/article/view/5886/5379; Bernadette McSherry, ‘It’s a Man’s World: Claims of Provocation and Automatism in ‘intimate’ Homicides” (2005) 29(3) Melbourne University Law Review 905 https://classic.austlii.edu.au/au/journals/MelbULawRw/2005/28.html ↩︎
16. Colin Howard, ‘Automatism and Insanity’ (1962) Sydney Law Review 36 https://classic.austlii.edu.au/au/journals/SydLawRw/1962/3.pdf; Bernadette McSherry, ‘Case Note: The Queen v Falconer (1990) 171 CLR 30’ (1991) 18 Melbourne University Law Review 476 https://www.austlii.edu.au/au/journals/MelbULawRw/1991/30.pdf. ↩︎
17. Maurice M Ohayon, Mark W Mahowald and Damien Leger, ‘Are Confusional Arousals Pathological?’ (2014) 83(9) Neurology 834 https://www.neurology.org/doi/10.1212/WNL.0000000000000727. ↩︎
18. See R v Youssef (1990) 50 A Crim R 1; Queen v Falconer (1990) 171 CLR 30; R v DB (2022) 108 NSWLR 51. ↩︎
19. Australian Law Reform Commission, ‘Traditional Rights and Freedoms— Encroachments by Commonwealth Laws’ (Report No 129, December 2015) 17 https://www.alrc.gov.au/publication/traditional-rights-and-freedoms-encroachments-by-commonwealth-laws-alrc-interim-report-127/11-burden-of-proof/a-common-law-principle-7/. ↩︎
20. See, eg, The King v Mullen (1938) 59 CLR 124, 128 (Latham CJ). ↩︎
21. The most important of these in Australia has arguably been R v Falconer (1990) 171 CLR 30; see also R v Quick and Paddison [1973] QB 910, 922 (Lawton LJ). ↩︎
22. See discussion of the rule that ‘a malfunctioning of the mind of transitory effect caused by the application to the body of some external factor such as violence, drugs, including anaesthetics, alcohol and hypnotic influences cannot fairly be said to be due to disease’ from R v Quick and Paddison [1973] QB 910, 922 (Lawton LJ) in Williams (n 14). ↩︎
23. R v DB (2022) 108 NSWLR 51. ↩︎
24. See Mental Health Impairment Forensic Provisions Act 2020 (NSW) (‘MHCIFP Act‘). ↩︎
25. Ibid s 4(1)(a), specifically the words ‘temporary or ongoing disturbance of … volition.’ ↩︎
26. See submissions of the applicant in The King v DB [2022] HCATrans 230 (16 December 2022) https://www.austlii.edu.au/cgi-bin/viewdoc/au/other/HCATrans/2022/230.html (‘Yes, we say that it does have significant impacts despite the fact that the legislation is New South Wales legislation…’). ↩︎
27. See MHCIFP Act (n 24) ss 28, 30. ↩︎
28. Ibid s 28; see also Judicial Commission of New South Wales, ‘Defence of Mental Health Impairment or Cognitive Impairment’, Criminal Trial Courts Bench Book (79th rev ed, December 2024) [6-230] https://www.judcom.nsw.gov.au/publications/benchbks/criminal/mental_illness.html. ↩︎
29. See, eg, Todd Davies et al, Practitioners Guide for Mental Health: A Guide to Assist Lawyers and Registry Staff to Understand and Navigate the Mental Health Forensic Processes (Guide, February 2022) https://publicdefenders.nsw.gov.au/documents/resources-and-papers/guide-to-mental-health-forensic-processes/practitioners-guide-for-mental-health.pdf. ↩︎
30. R v DB (2022) 108 NSWLR 51. ↩︎
31. Ibid 70 [56] (Brereton J). ↩︎
32. Ibid 94 [192] — [196] (Wilson JA). ↩︎
33. See, eg, RJ Sutton, ‘Automatism and the Drunken Sailor: Four Practical Problems’ (1966) Otago Law Review 156 https://www.nzlii.org/nz/journals/OtaLawRw/1966/6.html. ↩︎
34. Ibid 164. ↩︎
35. See, eg, Brendon Murphy, ‘Pushing the Boundaries of Automatism witbh Sexsomnia: ‘R v DB’ (2023) 47(1) Criminal Law Journal 376. ↩︎
36. See Collen Davis, ‘Sexsomnia – Excusable or Just Insane?’ (2015) 39(1) Criminal Law Journal 21. ↩︎
37. Jennifer M Mundt et al, ‘Behavioral and Psychological Treatments for NREM Parasomnias: A Systematic Review’ (2023) 111 Sleep Medicine 36 https://linkinghub.elsevier.com/retrieve/pii/S1389945723003271. ↩︎
38. See Alon Y Avidan et al, ‘Hand Dominance Shift during Sleep in Sexsomnia: A Clue to Pathophysiology?’ (2025) Journal of Clinical Sleep Medicine jcsm.11554 http://jcsm.aasm.org/doi/10.5664/jcsm.11554. ↩︎
39. McSherry (n 15) 928–9. ↩︎