Final answer:
Having more REM sleep than usual could be related to intensive learning activities during the day, a REM rebound effect after sleep deprivation, or could serve as emotional processing. While narcolepsy is associated with REM sleep, it doesn't typically cause increased REM sleep during the night without prior sleep deprivation.
Step-by-step explanation:
If you experience more REM sleep than usual in a single night, it may be because of several reasons. One potential reason is that you have undergone a learning-intensive day. During learning and memory consolidation, REM sleep appears to play a significant role, which could lead to an increase in REM sleep following a day of significant cognitive engagement. REM rebound, another factor, might cause an individual to spend more time in REM sleep following periods of sleep deprivation. As for narcolepsy, this sleep disorder intuitively involves symptoms resembling REM sleep and can include sudden transitions into REM sleep during the day, but experiencing more REM sleep at night as a function of narcolepsy alone without evident sleep deprivation during preceding days seems less likely to directly cause an increased duration of nocturnal REM sleep.
REM sleep is essential for processing and regulating emotions. A heightened period of REM sleep, especially under non-stressful conditions, may serve as an adaptive response in helping manage emotional salience from events that occurred during wakefulness. Therefore, if you have been under stress or have had emotionally charged experiences, you may also find yourself with an increased need for REM sleep to help process those emotions.