Ever sit in a class or at work, get bored, look out the window and the next thing you know 30 minutes have gone by? When it happens within 'normal' limits we often call it day dreaming... our mind goes off someplace else.
For those of us with dissociative disorders we do it more frequently, we do it to escape, we can find ourselves someplace different without knowing hoe we got there, other personalities can come out and 'take over'.... There are a bunch of different ways that this same kind of thing is more severe and begins to cause problems in every day life... more than missing half a class of notes or pissing off the boss for the moment.