When most people suffer through a poor night of sleep they feel sleepy the next day.This response may seem too trivial to merit comment ,yet it represents perhaps out main defense against chronic insomnia. Sleep is supposed to be self-correcting: sleep loss increases the drive for sleep; it incurs a "sleep debt" . This debt should be experienced as increased sleepiness during waking hours.It should then lead to more sleep of deeper intensity when dedtime rolls around again, which in turn should pay back the sleep debt.