Sleep Calculator

When sleeping, the mind uses much less power compared to being alert - especially in non-REM phases. Eyes dart around during REM rest, muscles shut down almost completely, dreaming shows up. That stage carries traits distinct from quieter, deeper non-REM cycles. One kind hums with activity while the other moves slow and still. These two forms of slumber feel worlds apart. Every so often, the body shifts between non-REM and REM sleep roughly every hour and a half, cycling four to six times when rest goes well. Starting off with non-REM, it drifts later into slow-wave stages - deep rest kicks in here. As that happens, heat levels dip, heartbeat slows down too. The mind burns much less fuel during this phase, busy refilling its stockpile of ATP, the compound storing and delivering energy within cells. In these quiet hours, growth hormone flows out, playing a key role in how people grow. Most of the night people spend less time in REM sleep. Dreams tend to happen during these moments, sometimes scary ones. Missing out on this phase might lead to restlessness, trouble focusing, odd thoughts, even seeing things that are not there. After being blocked from reaching REM, the following nights often show more tries to enter it, along with longer stretches inside it than before. That response has been named REM rebound, hinting at how vital this stage could be. Scientists continue exploring what exactly happens here, why it matters so much. While experts generally agree it plays a key role, there are rare times when skipping parts of it briefly seems to bring short-lived benefits.