Asleep — with an active brain.
REM stands for rapid eye movement. Your eyes move beneath closed eyelids, and brain activity can look surprisingly like wakefulness.
Open three windows into REM.
Your brain
Brain activity is high. REM is linked with learning, memory and the processing of emotions; these functions also involve other sleep stages.
Your dreams
Vivid dreams are common in REM. Dreaming can also happen in non-REM sleep. Remembering a dream is not a reliable measure of how much REM you had.
Your body
Most skeletal muscles are temporarily much less active. Breathing and heart rate may become more variable. Your body is still asleep, even though your brain is busy.
You remember no dreams. Does that prove you had no REM sleep?
Read the explanation
You may forget dreams or not recall them when you wake. A dream diary cannot tell you the stage-by-stage structure of your night.
The end of the night
is still part of the story.
REM periods tend to get longer later in the night. Cutting sleep short can remove some of that opportunity — even when you already had deep sleep earlier.
A friend wants to “maximise REM” and ignore the other stages. Is that a useful aim?
Read the explanation
REM is important, but it is not a substitute for non-REM sleep. Giving yourself enough opportunity for sleep supports the whole pattern.