At 3 o'clock in the morning, John has already slept for 4 hours. As long as his sleep continues, we can expect an increasing occurrence of

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At this point in the sleep cycle, John would have already gone through Stage 1, Stage 2, and some Stage 3 sleep. As he continues to sleep, he will enter more frequent periods of REM sleep. This is because as the night progresses, the duration of REM sleep increases while the duration of Stage 3 and 4 sleep decreases. Hypnagogic sensations and muscle tension usually occur during Stage 1 and 2 sleep, while Stage 4 sleep usually occurs earlier in the night and is less common later on.

At 3 O'clock in the Morning, John Has Already Slept