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Sleep apnea, the most commonly diagnosed sleep disorder in the US, is "lawyers' new favorite criminal defense," according a recent New York Post article. The gist of the sleep apnea defense is: "I'm not guilty for my actions because, due to my sleep apnea, I suddenly fell asleep before doing whatever I was accused of." As legal defenses go, this one has a relatively short history — it only dates back to 1994, when it was (unsuccessfully) invoked in a murder trial. But, over the past four years, the Post reported, "sleep apnea has become the go-to diagnosis in defending against cases of fatal car and train crashes."

Is the sleep apnea defense a valid excuse for illegal behavior or a cheap way to dodge culpability? It depends on whom you ask. But experts say there are instances where the sleep-breathing disorder does cause otherwise responsible people to commit dangerous acts. A solid sleep apnea case should be provable and, in some cases, relatively straightforward to argue. To understand the sleep apnea defense, it might be useful to compare it to another sleep-crime defense, the notoriously incredible (as in hard-to-believe) "sleepwalking defense."

The sleepwalking defense is not like a fine wine. It is old, but it hasn't improved with age all that much. The defense dates back to 1846, when Massachusetts man Albert Tirrell successfully convinced a jury that he killed a prostitute and burned down her brothel in an unconcious, and therefore blameless, state. (I explored the evolution of the sleepwalking defense back in 2015, here.) There was no way for Tirrell to prove, retroactively, that he was sleepwalking when he said he was. But the jury believed his story and Tirrell walked free. 

The sleepwalking defense is not like a fine wine. It is old, but it hasn't improved with age all that much.

Modern-day sleepwalking cases aren't all that different from Tirrell's. We know a lot more about sleepwalking and other abnormal sleep-movement disorders, called parasomnias, which are thought to occur during deep sleep. For instance, researchers have identified behaviors that trigger sleepwalking episodes and brain activity patterns that are characteristic of those episodes. But, even with more knowledge and fancy tools, there's still no way to show with certainty that someone sleepwalked at a specific time in history. To make a sleepwalking case, a defendant can show a personal history of the disorder. They can also undergo clinical sleep tests to record electrical brain activity during deep sleep. And, on the off chance they sleepwalk during their sleep test, they'd be able to offer polysomnographic recordings as evidence that they do, in fact, have a habit of unconsciosus roaming. Some experts contend that this evidence is sufficient to corroborate a sleepwalking defense. But, in court, the defense fails far more often than it succeeds. And it's ultimately a flawed method of absolution. 

"After the fact, it's virtually impossible to quote-unquote prove that someone was unconscious and not in control at the time that they did whatever they did," said Stephen Poceta, a neurologist who’s provided expert testimony at sleep-crime trials and has written about Ambien-fueled sleepwalking episodes.

The sleep apnea defense, on the other hand, is sturdier. Sleep apnea is a medical condition that can be tested for. Sleepwalkers probably won't sleepwalk during a sleep test. But sleep apnea sufferers will most likely exhibit symptoms of the disorder (snoring, breathing gaps) whenever they doze off. And sleep apnea does affect daytime functioning, leaving sufferers more likely to get drowsy and fall asleep during their normal activities, said Poceta. Unless it's a very mild case, diagnosis should be fairly cut-and-dry.

Forensic sleep expert Mark Pressman emphasized the abnormal speed with which apnea sufferers fall asleep: "They'll claim to doctors that they feel alert," he told the Post. "But their performance will be poor when tested. And when told to fall asleep, they’ll do so, however fitfully, in a minute or 2 flat, as opposed to the 15-to-20 minutes it takes for a healthy person." 

Awareness is the crux of the sleep apnea defense in the UK.

So, provided a defendant has all the pieces to plead their case, they should be able to put them together to show cause and effect. The prime example of a strong sleep apnea case is the same one that arguably catapulted the defense into mainstream consciousness: In 2013, William Rockefeller, a Metro North train engineer, fell asleep on the job. A resulting derailment killed four people and injured more than 60. Rockefeller was later found not guilty due to undiagnosed sleep apnea. This accident and others have lead to the expansion of mandatory sleep apnea screenings for public transit engineers and conductors.  

But, that doesn't mean the sleep apnea defense is always a slam dunk or that it can't be twisted beyond the point of believability. In another case, mentioned by the Post, a man groped a woman sitting near him on a plane. He claimed that he mistook the woman's breasts for pillows during a state of groggy confusion that was exacerbated by his sleep apnea. This is an example of confusional arousal, said Poceta (who didn't work on the case). Essentially, a rocky transition from sleep-to-wake leaves someone disoriented and subject to unsavory behavior like groping a stranger or firing a gun. An apnea-based confusional arousal is a harder sell than a simpler driver-falls-asleep case. But, Poceta said, sleep apnea can make the sleep-to-wake transition harder. And, years ago, Poceta did help get a defendant out of a murder charge using this argument. 

Another factor is awareness of the condition. Rockefeller (the train conductor) hadn't been tested for sleep apnea during his most recent medical screening. So he was able to argue that, since he didn't know he had the disorder, he had no reason to suspect he was more vulnerable to falling asleep than any other conductor. Awareness is the crux of the sleep apnea defense in the UK, said Chris Idzikowski, an expert witness in sleep crimes.

"OSA (obstructive sleep apnea) itself in a sleep-related road traffic collision is not a defense," said Idzikowski. Though, generally, people are not responsible for what they do when they're unconscious, there are exceptions. Someone can be held accountable for unconscious behavior if it's proven they knew (or should have known) they might fall asleep. The laws regarding culpability for unconscious behavior vary from country to country. Idzikowski said that all sleep-related cases are difficult both from a prosecution and a defense standpoint. But he has noticed a rise in the use of the sleep apnea defense. 

If the sleep apnea defense is indeed having a moment, let's hope the attention leads to fewer missed sleep apnea diagnoses among train engineers, and other workers for whom falling asleep on the job poses a direct public safety hazard.