Sleep debt is the amount of sleep you should have had, but didn't. Many people can accumulate 30 or 40 hours of sleep debt, and still they think they are functioning normally during the day!  But doctors can show that such a person is impaired. Their reactions are not as quick as they could be, their memory is not as good as it should be. If they are put in a quiet situation, with no stimulation, they will easily fall asleep. The test of how easily someone can fall asleep is known as a "sleep latency test". When done several times during the day, it is known as a "multiple sleep latency test", or MSLT.

Sleep debrivation causes you to feel tired (not sleepy). Most people describe this feeling as tiredness. If you lower your sleep debt, the feeling of being tired every day goes away.

Some researchers say that they have never seen a case of "chronic fatigue syndrome". Some researchers feel this is just a fancy name for not getting enough sleep. Often that individual has very real sleep problems that need to be taken care of. But once they are, the fatigue goes away.

Sleep debt is easy to camoflauge. To find it's hiding place, you have to strip away the things it hides behind, like stress, activity, and other stimulations... Try sitting down in a chair on a warm afternoon, in the sun. Relax. If you start to feel tired, or drowsy, and can fall asleep, you have a sleep debt.

On the other hand, someone without a sleep debt, can not fall asleep, no matter how boring the surroundings!

Q: How do you know if you have a sleep debt? 

A: That's easy:

If you feel tired during the day, you probably have a sleep debt. You don't need to go to a sleep clinic. Just sit and relax quietly in the afternoon in a peaceful place. If you feel the need to go to sleep, then you have a sleep debt. Try keeping a sleep diary.

Q: What are some of the ways that we accumulate a sleep debt?

A: One of the easiest ways to accumulate sleep debt is to use an alarm clock. If you regularly need your alarm clock to awaken at the right time in the morning, you are probably incurring a sleep debt every time it wakes you up.

Q: Can I accumulate a sleep surplus?

A: Unfortunately, we can not. When your body does not need sleep anymore, you will not be able to sleep!  Some people feel tired after sleeping in late. This probably shows that they still have an accumulated sleep debt. Probably only one person in a thousand gets down to the point where they have no sleep debt. By sleeping extra time one day, you can put a small dent in your sleep debt. The drowsiness that you feel is an artifact of laying in one place for a longer time, and probably also that the biological clock is less active at the time you have awakened.

Q: Can too low of a sleep debt cause problems?

A: Sleep debt is an important factor in falling asleep and remaining asleep all night. Sometimes, when an individual makes a concerted effort to get extra sleep and payoff their sleep debt, eventually they can begin to have problems getting to sleep at night, and staying asleep at night. When this happens, the individual is probably getting close to the optimum amount of sleep each day. At that point, the individual should slight reduce their daily sleeping time, by 15 to 30 minutes.

Other interesting resources:

Debt, neck support, back support, mattresses, blankets, pillows