What is Sleep debt?

Sleep debt is a term used to describe the physiological phenomenon by which a person who has not had his usual quota of sleep for some time compensates for the lost sleep. A few hours of sleep everyday is a must for all. If a person who usually sleeps for 6-8 hours a day goes without sleep for a few days, he would sleep for much longer hours when he next goes to sleep. The more the number of days he is deprived of sleep, the longer will be the duration of the compensatory sleep. This proportionate increase in the hours of sleep in relation to the hours of sleep lost is due to sleep-debt. It is as if the body keeps count of the number of hours of sleep lost and makes up for it by going to sleep for proportionately longer periods.