That happened to me a few weeks back. She is always active at the same times every day and every night. She's most active around midnight and she had been calm most of the day and I went to bed and she wasn't moving and I got freaked out and called my OB. I went to L&D to be monitored and she ended up being fine. Just resting. Try drinking a glass of orange juice or have something sweet and lay on your side for 20 min. That should get her moving and if it doesn't and she hasn't moved for 2 hours, just give your OB a call. It can't hurt.