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

Over the past decade, “sexsomnia” has been used as a defence in a number of Australian sexual assault trials.

This sleep disorder – sometimes known as “sleep sex” – causes people to engage in sexual behaviour while asleep.

Last week, a Sydney man with sexsomnia was acquitted of rape charges. 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. 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. 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. 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. It sits alongside sleepwalking and night terrors.

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

It’s unclear how common sexsomnia is, but it’s thought to be rare. A 2020 study found only 116 clinical cases had been recorded in the medical literature.

But it may also be underreported due to embarrassment and a lack of awareness.

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.

Automatism describes actions without conscious volition (meaning without using your will). 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.

But an important debate in the legal cases, as well as among psychiatrists and sleep experts, is about how to classify the condition.

Essentially, is sexsomnia a mental health impairment caused by an underlying mental illness? 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.

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.

By contrast, the prosecution must prove “beyond a reasonable doubt” that the sexual acts were voluntary or “willed” – a higher standard of proof.

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 cases have considered whether the law should treat sexsomnia as an ongoing mental disorder instead of a transitory “malfunction of the mind”.

In a 2022 case, prosecutors accepted that a New South Wales man accused of sexual offences against his daughter had sexsomnia. 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.

In defining mental health impairments, the new laws included a disturbance of volition.

Why is this significant?

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

If the prosecution could establish sexsomnia was a mental health impairment, then an outright acquittal would be unlikely.

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

However, the prosecution in the 2022 case failed to establish sexsomnia was the result of a mental health impairment under the new laws. A two-judge majority said sexsomnia was not a “disturbance of volition” because no one has volition when they are asleep.

The dissenting judge 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”.

Why are these definitions controversial?

As long ago as 1966, legal scholars criticised how the law treats different kinds of automatism.

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.

Whether sexsomnia is a sleep disorder with non-recurring episodes or a more permanent mental disorder continues to be debated.

However the way it 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.

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.