not feeling the baby move anymore.... 21 weeks

For the past two weeks, there have been very few waking moments where I HAVENT felt the baby move, kick, punch, stretch, cha-cha, polka, or try out hip-hop or whatever else goes on in there. Now for the past 36 hours I haven't felt anything. I've read that the baby can move into a position that makes its movements very hard to feel. But when you've miscarried before, there's just nothing as reassuring as your baby moving and letting you know it's alive and well. I'm just not sure what to think. Please help.