Most days, we go about 16-18 hours without sleep. Then our biological rhythms compel us to hunker down and get some shuteye.
But what if you refuse? Or, worse, what if you're unable to sleep?
This is the question that inspired some grueling sleep deprivation experiments in the 1950s and 60s.
Perhaps the most famous is the world record set by the New York DJ Peter Tripp. He stayed awake for 201 hours (8.4 days). He spent most of the ordeal in a glass booth in Times Square, and the rest in a hotel room across the street being monitored by scientists.
After three days, Tripp began laughing hysterically at nothing at all. He also became upset, confused and paranoid.
He hallucinated - at first, simple patterns like cobwebs on people's faces, or insects which were really specks of paint on the table. But soon, they became more intense, like waking dreams. He famously saw mice and kittens scurrying around the room.
By the end of his sleepless stunt, Tripp actually became psychotic. He rummaged through draws searching for non-existent money. He accused a technician of trying to harm him. He then claimed he was not Peter Tripp but an impostor. Nothing made sense to him.
On reaching his 200-hour target, Tripp was made to stay awake for one final hour while doctors did more tests. They left the EEG in place as he finally closed his bloodshot eyes and entered a deep 13-hour slumber.
Unfortunately, there were permanent consequences to the experiment. Tripp's family noticed a difference in his personality; he was moody and depressed. He fought with his boss, became involved in the Payola scandal, and was fired from his high profile job. He went on to have four divorces.
Some would say the 8-day stunt changed Peter Tripp forever.
We all need nightly sleep to function normally. But there are plenty of things that get in the way of this: working night shifts, traveling through multiple time zones, sleep disorders like insomnia, stress, depression, the menopause, and in extreme cases, interrogation and torture.
Needless to say that prolonged sleep deprivation can take a huge personal toll.
Despite this, we all go through it at some point or another. An increasing number of us are chronically sleep deprived because of our modern lifestyles. And the cost of that sleep deprivation on society is thought to be massive.
American businesses are thought to lose $100 billion in productivity each year. Even worse, tired workers are thought to be responsible for disastrous assaults on nature - ranging from the giant oil spillage of the Exxon Valdez, to the nuclear meltdowns of Three Mile Island and Chernobyl.
The effects of sleep deprivation start small and soon run wildly out of control. Physically, emotionally and cognitively, the impact is increasingly debilitating.
And if you go for long enough without sleep, the result is deadly.
This is the case for sufferers of a disease called Fatal Familial Insomnia (FFI), a rare and incurable sleep disorder that causes total sleeplessness. Starting sometime in middle age, sufferers go to bed one night and are completely unable to switch off consciously. Sleep never returns.
After around 18 months of insufferable sleeplessness, moving through phases of panic attacks, hallucinations, weight loss and dementia, death is inevitable. Read more about the discovery of this tragic neurological condition in D T Max's The Family That Couldn't Sleep.
In the name of science, volunteers have gone for days without any sleep at all, while researchers measured the mental and physical effects of sleep loss.
Here's another intriguing case from the Guinness World Records.
In 1964, a 17-year-old high school student named Randy Gardner beat the world record for sleep deprivation by staying awake for 264 hours (11 days) without using any stimulants.
The effects of sleep deprivation on Gardner were less extreme than on Peter Tripp but still included moodiness, problems with concentration and memory, paranoia and hallucinations.
After four days, he had the delusion that he was a famous American football player winning the Rose Bowl. He also mistook a street sign for a person.
On the 11th day, he was asked to subtract seven repeatedly, starting from 100. He stopped when he got to 65... and said he had forgotten what he was doing.
Yet later that day, Gardner held a press conference in which he spoke without slurring his words and appeared to be in excellent health.
After his marathon, Gardner slept for nearly 15 hours and returned to a normal sleeping pattern within days.
Unlike Tripp (who, incidentally, used stimulants to stay awake) there were no reports of any long term personality changes.
Much to Gardner's displeasure, within a month of setting his sleep deprivation record, Toimi Soini of Finland stayed awake for 276 hours (11.5 days).
And in 1977, Maureen Weston of the UK went without sleep for a massive 449 hours (18.7 days). She began to hallucinate towards the end but reported no lasting effects from her rocking chair marathon.
However, if you're planning a sleep deprivation stunt of your own - forget it.
Guinness World Records no longer recognizes this category because long term sleep deprivation is thought to pose serious health risks, both physically and mentally. It could even trigger other sleep disorders, not to mention long term personality changes like those displayed by Peter Tripp.
What's more, they point out that sufferers of chronic insomnia could be staying awake for far longer than these formal record attempts.
What a shame that the UK's Tony Wright didn't know this when he stayed awake for 266 hours in 2007. He thought he was outdoing Randy Gardner, and hadn't even heard of Toimi Soini.
A spokesman for Guinness World Records simply said: "People who attempt records should make sure their research is accurate or they may be very disappointed."
To learn more about this fascinating subject visit the website End Your Sleep Deprivation by the father of sleep medicine, Dr William Dement, and his students at Stanford Sleep and Dreams.
I was walking down a hallway with my dad when it happened. A dark, pointy figure grabbed me by the ankles and flung me down the hall. I was shocked and in pain. But before I knew what was happening, he marched over to me and did it again. He was furious. He was going to destroy me. And I had nothing. Except for my lucidity.
Members of our lucid dream forum have been asking how to create dream characters in lucid dreams. The most common problem is having characters who look nothing like they should. Or they seem disinterested in your company. Or they fail to show up on command altogether. So, how to combat this? It's a matter of finding creative solutions that bypass logical expectations.
To lucid dream, I recommend being able to remember at least one vivid dream per night. That will boost your self awareness in dreams (making lucidity more likely) and also means you can actually remember your lucid dreams. Which is nice. Here are four detailed tips on how to remember your dreams more frequently. And if you don't think you dream at all - trust me, you almost certainly do. It takes an extraordinarily rare sleep disorder to deprive someone of dream sleep.
It is estimated that these wise and wily Indians have been using mugwort in their healing and ritual practices for 13,000 years, where it is known as the ‘dream sage’. They use the herb to promote good dreams, which they consider an essential aspect of normal human functioning! But that’s not all...
Silene Capensis has been used for millennia by the Xhosa shaman of the river valleys in the eastern cape of South Africa, where it is known as Undela Ziimhlophe or 'white paths'. It's fragrant white flowers open only at night, when they emit a fragrant and almost hypnotising aroma. Also known as African Dream Herb or Ubulawu, Silene Capensis induces spectacularly vivid dreams - yet has never entered the mainstream and remains a fringe taste within western culture.
Experts agree that everyone is capable of having lucid dreams. Dreaming itself is a normal function of the mind. We all dream every night, even if we don't remember. And we all achieve conscious awareness while awake every single day. So what does it mean to combine these states? Why, the amazing ability to have conscious - or lucid - dreams. Sounds simple, doesn't it? So why do I keep hearing from people who say they can't achieve their first lucid dream?