Quote Originally Posted by Thor View Post
REM dreams are generally more vivid, and NREM dreams are generally more thoughtlike, so if you have a vivid dream it's most likely a REM dream, and if you have a thoughtlike dream it's most likely an NREM dream. However, a significant proportion of REM dreams are thoughtlike, and a significant proportion of NREM dreams are vivid. Yet, people do not act out vivid NREM dreams. (Well, they do in sleepwalking and night terrors, but those are anomalous anyway.
Not convinced by that Thor. Most of what I've read indicates that NREM and REM dreams are quite different.

Quote Originally Posted by Thor View Post
I think asking why we have atonia only in REM sleep is the wrong question. In my opinion a more interesting question is: what is it about REM sleep that causes the brain to transmit nerve impulses to make the limbs move, thereby necessiating REM atonia?
The interesting answer is this: the fact that in REM you are inhabiting a 3D virtual world and so moving through it. Atonia stops your dream movements translating to real life.

Quote Originally Posted by Thor View Post
As an aside, I don't understand why you say "thoughtlike or daydreaming", because daydreaming is very immersive and quite the oppsite of thoughtlike.
Not really. Daydreaming is thinking. You can visualise whilst daydreaming, and I'm sure you can even visualise a model of yourself within daydreams.
But you do not inhabit the day dreams. Which in my mind is the critical difference.