What does sleep disorder actually mean?

Many things: Sleep disorders include sleep apnea, sleep paralysis, sleep talking, walking and eating, bedwetting, jumping leg syndrome, repeated nighntmares or night terrors, insomnia andf/or frequent awakening. So'me, if not all, occur in rem sleep and this is the most important part of the sleep cycle. If deprived of it for long enough, it is lethal. A sleep laboratory can define.