This happened to an alt in the previous Venthyr assault. I think something about how the character lands triggers an anti-hacking disconnect. Of course, that’s a legitimate bug, since something an NPC does to you shouldn’t cause a disconnect.
Anyway, to retrieve the character, use the self-serve Character Stuck service. It’ll get you out of the disconnect loop. When I had to use it, it put me outside the gates of Orgrimmar (which is fine for my Horde character) and dead (because it was apparently a killing fall) but no other consequences.
Click the big “Character Stuck” button at the bottom of the page.