This sequential expression followed the phases of the traditional cell cycle: G0/G1 (the cell grows larger), S (the cell replicates its DNA), and G2/M (the cell prepares for division and then splits).

and 4 stages that make a complete cycle. You’ll typically complete 4 to 6 cycles per night. The first 3 stages, part of the first phase, are called non-REM sleep (N1 through N3). The final stage ...