REM sleep is an essential component of sleep, and REM rebound is the evolutionary mechanism by which the brain recovers a deficit. After early research established that REM makes up approximately 20% of normal human sleep, experimenters began selectively depriving subjects of REM to test its unique importance. Whenever EEG and eye movement readings indicated REM onset, subjects were woken for several minutes. As deprivation continued, the tendency to initiate REM increased — subjects had to be woken more frequently each night. The effects were pronounced: subjects became irritable, anxious, and hungry, and several left the study early. When finally allowed to sleep undisturbed, REM percentage jumped from an average of 19.4% to 26.6% — a significant rebound compared to a control group woken an equal number of times at random intervals.

A first-of-its-kind Sleeptracker-AI study of more than 6.8 million nights of sleep validates this deprivation-recovery cycle at population scale. Most people accumulate a REM deficit during the week and attempt to recover on weekends. The data show REM deprivation beginning on Sunday night and building progressively through the week, transitioning into a REM recovery cycle on Friday and Saturday nights — repeating consistently across the dataset.

Further reading:

What is REM sleep?
https://www.sleepassociation.org/about-sleep/stages-of-sleep/rem-sleep/

The importance of REM rebound and CPAP compliance
https://www.sciencedirect.com/science/article/abs/pii/S1389945712001864