Upon awakening in the morning, you usually lie in bed for 30 minute before getting up. In this example, you spend on average eight hours in bed and on average are asleep for six of the eight hours. Using the technique of sleep restriction, initially you would limit your time in bed to six hours. The main effect of sleep restriction is to produce mild sleep deprivation, which will help you fall asleep faster, stay asleep longer without awakening, and sleep more deeply. Your total sleep time may not increase, but the quality of your sleep will improve.
Daytime sleepiness is a normal but temporary side effect.