What are sleep stages?

During a sleep session, your body repeatedly cycles through light, deep and REM (rapid eye movement) sleep, as well as short periods awake which you might not even be aware of. Depending on the duration of the sleep session, you will move through up to five sleep cycles, each lasting about 90 minutes on average. Each cycle usually starts with light sleep, followed by deep sleep, REM sleep, and ends with a brief period awake. However, sleep cycles are not necessarily all the same; the early part of your night consists of more deep sleep and the later part more REM sleep. Your transitions between sleep stages and time spent in each of the sleep stages are visualized in a hypnogram in the app.