And there is a tendency to boast about needing little sleep to function. Margaret Thatcher and Ronald Reagan were said to survive on a few hours a night. Both developed dementia in later life.

“We have stigmatized sleep with the label of laziness,” Professor Walker said.

“We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting. It’s a badge of honor.

“When I give lectures, people will wait behind until there is no one around and then tell me quietly: ‘I seem to be one of those people who need eight or nine hours’ sleep.’ It’s embarrassing to say it in public.

“They’re convinced that they’re abnormal, and why wouldn’t they be? We chastise people for sleeping what are, after all, only sufficient amounts. We think of them as slothful.

“No one would look at an infant baby asleep, and say ‘What a lazy baby!’ We know sleeping is non-negotiable for a baby. But that notion is quickly abandoned [as we grow up]. Humans are the only species that deliberately deprive themselves of sleep for no apparent reason.”

Signs of a lack of sleep include needing caffeine to stay awake during the afternoon or wanting to sleep on after the alarm goes off.

“I see it all the time,” Professor Walker told the Guardian. “I get on a flight at 10 am when people should be at peak alert, and I look around, and half of the plane has immediately fallen asleep.”

He suggested people should set themselves an alarm 30 minutes before they should go to bed and start to wind down from that point.

The brain is actually extremely active while we are sleeping.

“During NREM [non-rapid eye movement or deep] sleep, your brain goes into this incredible synchronized pattern of rhythmic chanting,” Professor Walker said.

“There’s a remarkable unity across the surface of the brain, like a deep, slow mantra.

“Researchers were once fooled that this state was similar to a coma. But nothing could be further from the truth. Vast amounts of memory processing is going on.

“To produce these brainwaves, hundreds of thousands of cells all sing together, and then go silent, and on and on. Meanwhile, your body settles into this lovely low state of energy, the best blood-pressure medicine you could ever hope for.

“REM sleep, on the other hand, is sometimes known as paradoxical sleep, because the brain patterns are identical to when you’re awake. It’s an incredibly active brain state.

“Your heart and nervous system go through spurts of activity: we’re still not exactly sure why.”

The NHS warns sleep deprivation can have “profound consequences on your physical health”.

“One in three of us suffers from poor sleep, with stress, computers and taking work home often blamed,” its website says.

“However, the cost of all those sleepless nights is more than just bad moods and a lack of focus.

“Regular poor sleep puts you at risk of serious medical conditions, including obesity, heart disease and diabetes – and it shortens your life expectancy.

“It’s now clear that a solid night’s sleep is essential for a long and healthy life.”

Article condensed from Independent Minds for Dr. David Jensen