One very interesting research study, that gives interesting information about sleep, was not originally intended to be sleep research.

This research project was intended to study the relationship between length of day and mood. You may have heard the theories that in the winter time, many people are depressed because of the reduced length of the day. This researcher was trying to see if shortened exposure to light would cause bad effects on mood. Subjects, were asked to spend 14 hours a day in absolute darkness. The length of the study was about a month. During the time in the dark, the subjects had absolutely nothing to do.

One of the most interesting aspects of the study, is that without external cues, and stimuli, the subjects started sleeping more. In fact, in the beginning, they were sleeping 12-13 hours a day. The length of time the subjects were sleeping then started to decline asymptotically, to 8 hours and 15 minutes. The extra sleep that they had was about 30 hours per person for a group of normal adults.

What about their mood?  Mood and energy levels in the group improved dramatically!

Most people can accumulate 30 to 40 hours in sleep debt, and still feel normal. Yet their impairment can be measured.  

How much sleep do you need?