Mine wasn't technically a "choking ghost," because I could breathe fine. There wasn't a 30 second time limit, either, but I could be a bit biased because I was probably dribbling adrenaline onto the bed. My room-mate thought it as a "night terror." This is really scary, actually -- a roomate once admitted to having night terrors that were so believable he'd wake up and be convinced that the dream was real. In fact, he had been known to throw items across the room in an attempt to slow down an "attacking" dream character. The scary part is that he slept with a .50 caliber Desert Eagle under his pillow with a chambered round. (shudder) I'll take "choking ghosts" any day.
Dan