I have been lucky. My only MU dreams I can recall have been either 'ooh good scene idea!' presumably inspired by whatever's going on on a given game, or...
...in the nightmare form, I am always coding. MUX coding, not wiki coding. (Sorry, Thenomain.)
(Wiki coding is a totally different set of nightmares.)
In the really horrible nightmare form, I am coding while a drama explodes and I have to mentally keep code and five or so people all having histrionic fits of flail at once that I have to mediate while everyone vaguebook snipes at each other in the peeves thread.
The above happened enough while asleep that I once had to erase 'fuck this, time to wake up' into a multi-page to the drama llamas before I hit enter, because it took a moment to remember, 'fuck, I'm awake :/' as it happened RL (sans peeve thread, iirc, but this was years ago).