As we move from stage 1 sleep to stage 4 sleep, the brain emits successively waves. smaller, faster larger, slower smaller, slower larger, faster

slower larger

A complete sleep cycle lasts between 90 and 110 minutes where your body passes through stages 1, 2 3, 4, and REM  where there is  "rapid eye movement".  Stages 1, 3, and 4 together account for r 30% of your sleeping hours, 20% REM and Stage 2 (50%).

As we move from stage 1 sleep to stage 4 sleep, the brain emits successively slower larger waves.

Stage 1 consists of very light sleep.  In this stage, your brain emits alpha waves (whose frequency ranges from 8 to 13 hertz) to theta waves (4–7 Hz).  The theta waves are slower and greater in amplitude (up-and-down movement).

In Stage 4, the brain emits almost all delta waves which are the slowest and highest amplitude brain waves.

i think it would be b the increase in body temp