Is 3 hours of REM sleep too much?

Your first period of REM sleep is generally only a few minutes long. For healthy adults, 20-25% of your total time asleep should be REM sleep. That's where the 90-minute number mentioned above comes from. If you sleep for 7-8 hours, 20% of that equates to roughly an hour-and-a-half, or 90 minutes.

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You can also ask how does lack of rem sleep affect you?

Physically, REM sleep loss is associated with increased inflammatory responses, increased risk for obesity, and memory problems. Patients with sleep apnea, which may be associated with a complete loss of REM sleep, are at increased risk for cardiovascular disease, diabetes, obesity, and depression. Is fitbit deep sleep accurate? Researchers concluded the Fitbit was equivalent to the actigraph in almost every way. Yet, when compared with polysomnography, the Fitbit was largely underestimating deep and REM sleep, missing roughly half of the former and a third of the latter. It also overestimated light sleep.