M'aiq suggests try to load a previous save.
Or it could of have been Serana's time, if you know what M'aiq means..
M'aiq also welcomes you to the forums. M'aiq wishes he had a stick made out of fishies to give to you. Sadly, he does not.
Was your weapon drawn when she fell out and attacked you? If so, sheathing it may fix the problem; occasionally, I accidentally hit her enough to get her to attack me, and when she does, sheathing my weapon causes her to cease attacking me.
If that's not it... I'm at a loss.
Here,raven400,Have a fishy stick http://i.imgur.com/G5fNGPE.jpg
Hmmm, never had this happen. New to me. I would reload to previous save or an auto one when you entered the tomb. I hope it turns out well for you. Welcome to the boards!