OBEs don't correspond with any particular brainwave pattern-- there's every pattern imaginable, including "wide awake" beta waves. This is why the whole "OBEs are just LDs" argument that's so popular on LD forums has no basis in fact.

Fred Aardema discusses OBEs that are really "out there" (mental plane? beyond F27?) and how certain bodily functions seem to slow or even shut down. Perhaps this is why Monroe's physical body was in distress during his later explorations.