I've noticed that I consistently experience vivid, visceral dreams when taking brief mid-day naps (usually ~20m at 8h after waking). They're not bad, just intense.
I wonder why—maybe I just remember them better during day? My night-time dreams are usually mild or absent.
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I have a very similar experience with mid-day naps (similar duration and time of day).
One factor that may or may not relevant is that I'm often
slightly caffeinated during the mid-day naps.
i.e. caffeinated but sleepy
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Ah, interesting. I think that's probably not the case for me: I arrange my caffeine intake to minimize caffeine during nap time (i.e. have coffee immediately on waking, no more until after nap @ ~8h). Of course with half-life at 6h some would still be there though…