Definitions of sleep terms from Cleveland Clinic:
REM Sleep: The stage where the brain is highly active; mentioned in “Why We Sleep” as critical for learning and memory consolidation.
Circadian rhythm: The body’s internal 24-hour clock, controlling sleepiness and alertness.
Sleep debt: The buildup of lost sleep across several days.
Partial sleep deprivation: Losing some sleep over several nights, which impairs cognition, mood and alertness.
Recovery sleep: The sleep taken to try to make up for lost sleep, which does not fully restore cognitive function if deprivation has been ongoing.
