Workout Session for sleeping

Hi, I want to develop the sleeping app which will wake up a user gently with low intense vibration if he has a nightmare. As far as i understand this can be done only via starting workout session before user goes to sleep and turning it off in the morning. The question is - Is it possible that apple won't approve the app for App Store because I use workout session not for workout. The second one - is there any other way to wake up a user?
Workout Session for sleeping
 
 
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