Crashing in the middle of the night?

I have been using and loving this app for a while. It works great. Except, lately, it has been somehow turning off in the middle of the night. Its happened four times now. I cant figure it out except the app is totally closed out and not even on when I wake up. Record shows it always stopping around 2:30am. Must be a bug? Doesnt wake me up in the morning!

Mark Walz about Sleep Cycle - Tracker & Sounds