REM rebound is the lengthening and increasing frequency and depth of rapid eye movement (REM) sleep which occurs after periods of sleep deprivation.
Sleep Deprivation: This refers to getting less than the necessary amount of sleep needed for optimal functioning.
Parasomnia: These are abnormal behaviors that occur during sleep, like sleepwalking or night terrors.
This is essentially your body's internal clock that regulates the timing of periods like wakefulness and sleepiness throughout the day.