Scientists believe that a nap can boost creative thought and help problem-solving. So what major breakthroughs in science and the arts have been made during sleep?
The old adage "I'll sleep on it" may have some truth in it, after all.
A study by researchers at the University of California San Diego has concluded that problems are more likely to be solved after a period of dreamy (rapid eye movement) sleep.
Scientists believe so-called REM sleep allows the brain to form new nerve connections without the interference of other thought pathways that occur when we are awake or in non-dreamy sleep.
Anecdotal evidence from some key figures in the arts and science suggests there could be some truth in this.
Here are some examples of major discoveries made in dreams.
Yesterday by The Beatles is one of the world's most well-known songs and according to the Guinness Book of Records, the song with the most cover versions.
Paul McCartney has spoken about how the melody came to him in a dream. He was staying in a small attic room in London in 1965, while the band were filming Help!.
He woke up with a tune in his head, he said, and immediately decided to play it.
"I got out of bed, sat at the piano, found G, found F sharp minor 7th - and that leads you through then to B to E minor, and finally back to E. It all leads forward logically.
"I liked the melody a lot, but because I'd dreamed it, I couldn't believe I'd written it. I thought, 'No, I've never written anything like this before.' But I had the tune, which was the most magic thing!"
He was still unsure whether he had merely repeated someone else's song so he played it to anyone who would listen, but no-one could identify it. Many fans have tried to do the same.
In the summer of 1816, Mary Wollstonecraft Godwin, 19, and her lover Percy Shelley, visited the poet Lord Byron at his villa near Lake Geneva in Switzerland.
In her dreams... and your nightmares
Weather frequently forced them and other guests indoors, where they read ghost stories, prompting their host Byron to challenge them to write one themselves.
Wollstonecraft Godwin, later Mary Shelley through marriage, has described how her famous work Frankenstein was inspired by a waking dream she had that night in Byron's villa.
In the introduction to the book, she explained what she saw: "With shut eyes, but acute mental vision, I saw the pale student of unhallowed arts kneeling beside the thing he had put together. I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half-vital motion."
The morning after her dream, she wrote what later became the first words of Chapter Five: "It was on a dreary night of November..."
THE NOBEL PRIZE-WINNING DISCOVERY
Dr Otto Loewi is described as the "father of neuroscience" and won the Nobel Prize for medicine in 1936. But that was the fruition of 16 years of work that began after one particularly productive night's sleep.
Robert Louis Stevenson's Dr Jekyll and Mr Hyde
Some have claimed Dmitri Mendeleev dreamed the periodic table but that's questioned
Samuel Coleridge's Kubla Khan was opium-induced
Friedrich Kekule's structural theory of atoms
The needles used by Elias Howe in his pioneering sewing machine came to him in a dream
The end of Handel's Messiah
Bram Stoker's Dracula
In 1903 the German had first had the idea that there might be a chemical transmission of the nervous impulse.
But in the years that followed he had failed to prove his theory, until Easter Saturday 1920, when he dreamt about it. He awoke in the night and made some notes, but the next morning he could not read his scribbles.
However, that night the idea returned to him as he slept. It was the design of an experiment to prove his theory, and it turned out to be the foundation for the work that years later won him the Nobel Prize.
THE WORLD-CLASS GOLF SWING
Even the sporting greats have the odd slump in form. In 1964, after rediscovering his touch following a run of poor scores, golfer Jack Nicklaus told the San Francisco Chronicle how it happened.
"Wednesday night I had a dream and it was about my golf swing. I was hitting them pretty good in the dream and all at once I realized I wasn't holding the club the way I've actually been holding it lately.
"I've been having trouble collapsing my right arm taking the club head away from the ball, but I was doing it perfectly in my sleep.
"So when I came to the course yesterday morning I tried it the way I did in my dream and it worked. I shot a 68 yesterday and a 65 today."
THE MATHEMATICAL THEORY
Indian maths genius Srinivasa Ramanujan was invited to Cambridge University in 1914 by English mathematician GH Hardy.
They collaborated productively for five years, making a series of breakthroughs, especially in number theory.
Mr Ramanujan claimed he drew inspiration for his analysis in his dreams.
He used to say that the Hindu goddess Namagiri would appear to him and present him with the formulae, which he would check after waking.
Below is a selection of your comments.
When I was doing my undergraduate degree at University, I had been working on a problem on solid mechanics as part of the final coursework. I had been trying to solve this problem for the entire day and finally i went to bed very tired without finding a solution. I remember I dreamt of this problem, and in my dream I was developing a methodology to solve it, step by step. When I wake up, I remembered my dream, including the mathematical operations required (not actually the calculations) and the data needed to be considered for the solution. I went to my desk and solved the problem in 15 minutes! I was really amazed.
Ed Hernan, Leeds
Such tales sound pretentious, unless one has seen this phenomenon in action. As a teenager, I commuted to work with my father, and he would explain solutions to mechanical and design problems that we had discussed only 10 hours before. He still 'works in his sleep', but most people now understand it is absolutely genuine. Sadly, this grand trait is not a genetic inheritance.
Kathleen Parsons, Ruislip, UK
The chemist Kekule said the structure of benzene, a six-carbon ring, came to him in a dream in which he saw a snake swallow its tail.
W. Jones Jordan MD, Acapulco, Gro., México
Tell us something new! I have been doing this for years and it is very true, I very often figure out projects and ideas when asleep, In fact I find my mind needs something to dwell on at night and hates to have an empty vacuum to dwell on at night and can get very depressed and morbid if allowed to wander. So I find myself looking for something to ponder and fall asleep to find it's solved in the morning.
Hmm.. it's a shame to point out that these are classic myths and there is evidence to show that they were stories concocted after the event to fit with popular conceptions of genius and creativity. Its certainly true that relaxing and thinking about something else can indeed help but some of the specific stories here aren't correct when you look at the historical records of the time. Rather like the many writers who claim that the words just poured out onto the paper from their mind, when later researchers discover stashes of earlier drafts!
Iain, Galway, Ireland
As every crossword solver knows, the last three or four clues that defeat you at night are obvious when you get up in the morning!
I have been thinking about aerodynamic drag theory as part of my PhD and got stuck on a problem. I stopped thinking about it for a few weeks because I did not know how to progress. A few days ago, with my brain in standby mode as I slept, the aerodynamic problem was solved all in the mind. I woke up, re-did the maths and hey presto the problem is solved. This is not the first time it has happened to me. The light bulb has come on many times in the last three years.
Anil Padhra, London/Reading
It's well-known that you wake up in the middle of the night with insights into logical problems. These have to be written down immediately - but very carefully so you can read/understand the idea the next day. Sometimes the answer is fatally flawed - but very often it is a neat lateral solution. It's worked for me in my successful trouble-shooting career for over 40 years.
A nice article, and the comments reinforce the view expressed. Earlier quite systematic studies suggest that the process may occur in a state of relaxation, often but not always just before sleep and waking. Other comfort zones may be culture dependent. Mathematical breakthroughs seem particularly susceptible through such a process.
Tudor Rickards, Manchester
I often wake up with the solutions to tricky programming problems I had been tackling the day before. Can I claim overtime for the extra hours spent working on the problem?
J Gurney, England