Deadman

She just fell asleep, all is fine...

jk she dead lol

But who killed her? probably the guy they talked about in the beginning or just the guy Annie was talking to.

It was obviously all planned by David - he sent his twin brother, then proceeded to scare the shit out of her and called him back when he confessed his love. She saw through all this and because he ruined her life, she decided to ruin his as well by telling him she wants him, then killed herself. He will suffer forever for his creepy way of asking her out on a date and she will haunt him for real in his memories.

BAM, debunked. No paranormal, just psychotic