Core sleep

Core sleep is sleep longer than a nap, usually defined around the 1 hour mark. Short cores usually contain one sleep cycle (90mins), going through all stages that are available in the current peak. Longer cores loop through several cycles, going through each vital stage once per cycle, with light-sleep in between. See repartition for more info.

By default, the body assumes all sleep to be cores, which means napping often needs to be learned first to become efficient.

A sleep longer than 50 minutes is usually classed as a core, though it may not actually end up being one until 1h or more. Any sleep shorter than 50 minutes is scheduled with the intent to be a nap (only one vital stage), which it almost always will be.

Cycles

Cores have cycles which are, by default, 1.5h long each, and contain all stages of sleep. compression is the process by which cycles change in length, which is part of some adaptations.

Cores should ideally be interrupted at the end of a cycle of within the first 30 minutes of one. This minimizes the chance of waking up during SWS.

Later cycles decrease more and more in sleep quality (Vital%), which is part of why more cores can have a similar efficiency gain to having naps, the other part being pressure management.

Default monophasic sleep contains 5 cycles (7.5h), with 8h being the result of +.5 extension, which usually contains REM or LS. 7h is also still considered 5 cycles as a result of anything above 45mins being considered a cycle. Therefore, there is a barrier at 6.75h where we assume 5 cycles, and one at 8.75h where we assume 6. Because these barriers are fuzzy, only e.g. 6.5h/7h are considered clear, with everything between being "4 or 5".