Muffin has had nightmare's before...she's actually yapped/barked in her sleep & it did not wake her up! She's never been aggressive though. I gently start rubbing her & talking to her. Then I start speaking louder until she's awake. When she "comes to" you can tell she has no idea what's going on, so I'm guessing she was just in an extremely deep state of sleep. Plus she ticked off that I woke her up!
CJ