It was whatever her and Mitchell saw when they died, no matter how brief it was!
Either way she didn't want George to know, cause she told him not to look when she opened the door to pass on!
OMG, guys okay, im rewatching the whole thing from the start and a few episodes later, saul is in the bar and terry wogan is talking to him for some reasson right, but he tells annie he nearly dies, and he was clinically dead for 6 minutes and he said he saw a really scary white light and men with sticks
I often wondered this myself. In the original pilot when Annie was sitting on the bed watching Mitchell sleep it was brought up and the subject quickly changed, so its gotta be something important if they keep teasing the audience like this.
I'm guessing its addressed further in the second series? I haven't seen it yet so I wouldn't know.
