What are sleep stages and why are they important?

During a sleep session, your body repeatedly cycles through light, deep and REM (rapid eye movement) sleep, as well as short periods of wakefulness 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.

These sleep stages are important because the duration and distribution of each sleep stage may reveal important information about a person’s mental and physical well-being. For example, individuals with depression characteristically demonstrate reduced deep sleep and increased REM sleep. Deep and REM sleep are particularly important in consolidating memories and play a role in cognitive performance. Research suggests that deep sleep is also involved in repairing damaged tissues and restoring energy sources.