Hi & yes this sounds familiar.
I once woke up 'in the middle' of a full attack, so know how strange and scary it can be.
It's odd as I always thought it was physiology directed by conscious state of mind (hence stress reaction) but as I wasn't having a bad dream, or any dream, on this occasion it was purely physiological.
I just found the reference that Celexa is citalopram, so interesting that I was on that when own episode occurred. One correlation doesn't mean it's definite, because the reason for being on it may be the cause, however it might be related. It's not a kind drug, I found it the hardest one to stop due to side effects turning me into a nightmare angry parody of myself.
It may be worth talking with your doc about it in case the amount can be reduced. As side effects don't generally get reported after initial trials, don't be suprised if they dismiss this possibility. Nobody warned me about withdrawal effects but I found plenty of personal accounts in online forums.
Like I said, not saying for sure it's the drug but at least you can do a bit more detective work about it. Hope it's a one-off bad experience for you.