Sleep cycles
There are five sleep stages in a cycle — wake, NI, N2, N3, and REM — which typically lasts 90-110 minutes. Research suggests that getting four to six cycles is ideal.
The best way to optimize your sleep cycle is to allot enough time for 4-6 90-minute cycles, and to try to plan your wakeup time to land during a lighter sleep stage to avoid higher levels of grogginess and fatigue upon awakening.