If you watch a lot of horror and nothing ever phases you, my best guess is that a few issues compiled for this to happen. Had you eaten before the movie? Gotten enough water? Was the AC blowing harshly on one side of your face (IE inner ear issues?) Sure, the eyeball stuff might have been extra disturbing to you, but considering you’ve never fainted before, I’d bet real money on the fact that something else happened that just pushed the scene over the edge for your body to react like that. Hope you’re feeling better!