It's been five days since Prince's death, but the exact cause remains a mystery. A preliminary sheriff's briefing discounted trauma and suicide, though the official autopsy report could take weeks before it becomes public.

In the meantime, possible comments from Maurice Phillips, who is married to Prince's sister, Tyka Nelson, are stoking speculation that sleep deprivation may have contributed to the musician's death.

Phillips reportedly told a crowd near Paisley Park, Prince's recording studio in Minnesota, that the musician had "worked 154 hours straight" in the days leading up to his death.

"I was with him just last weekend," Phillips is said to have told fans, according to the UK-based Press Association. "He was a good brother-in-law."

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Prince's longtime lawyer, L Londell McMillan, offered a different opinion. He said the death of the superstar was a complete shock and claimed the singer lived a clean and healthy lifestyle, disputing suggestions that he had a drug addiction.

McMillan said that while Prince may have been in pain and may have taken medication from time to time, he was "not on any drugs that would be any cause for concern".

"People use medication. The question is, are you on meds in a dangerous way?" he said.

McMillan noted that Prince, a vegan, was known for his clean lifestyle.

"Everybody who knows Prince knows he wasn't walking around drugged up," McMillan said. "That's foolish. No one ever saw Prince and said, . 'He looks high.' . It wasn't what he was about."

Prince had a famous work ethic and a penchant for recording at all hours of the day. Those close to the musician have remarked on his ability to get by on very few winks. No matter how good you are at playing the guitar at 4am, however, six days without sleep is a risky feat of endurance.

For the average person, a few days sans sleep can be enough to trigger hallucinations. And 154 hours edges toward the incredible. It's hard to say exactly who holds the record for prolonged sleep deprivation, but a strong contender is Randy Gardner.

Gardner, as a teenager in San Diego in 1964, went 264 hours without nodding off. He's the reigning holder of the Guinness World Record for length of time without sleeping - and he won't have to worry about defending the title.

The record-keeping organisation has since put the kibosh on the category, citing possible danger to participants. What scientists don't know about extreme sleep deprivation could fill volumes, because the act of depriving mammals from sleeping is so dangerous.

Reports are saying that Prince may have been sleep-deprived prior to his death. Photo / AP
Reports are saying that Prince may have been sleep-deprived prior to his death. Photo / AP

Take Allan Rechtschaffen's rats. In several rodent experiments in the 1980s, Rechtschaffen, a researcher at a University of Chicago sleep lab, kept rats awake as long as he could. In one study of 10 rats, the rodents went between 11 to 32 days without sleeping, before succumbing to slumber of the eternal kind.

Although the scientists could tell when the animals were close to death, it wasn't clear what, exactly, the rats were dying of. It's an academic debate that's continued to the present day. As Slate noted in 2009, there are a few possible causes for why the rats died - hypothermia, brain damage, too much stress, possibly bacterial infections following a critically lowered immune system.

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Even when it's not fatal, sleep deprivation is linked to a bouquet of ill effects. The Centers for Disease Control and Prevention has gone as far as to call lack of sleep - less than 7 hours of sleep in a 24-hour period - a public health problem, citing increases in depression, hypertension and risk of cancer.

Insufficient sleep can sneak detrimental tendrils into unusual aspects of life, with some researchers arguing it triggers false confessions and others saying it makes us more unethical. (Speaking of ethics, the United Nations called on the US military to end sleep deprivation among detainees, in a report condemning torture in 2014.)

Prince was superhuman in his ability to churn out musical hits. If it's true that he worked for six days straight, though, it's a sad reminder that even the incredibly gifted need to rest.