This doesn't happen all the time, Actually I haven't had this for a few years (i used to get it almost everyday)

But i'm starting to fall asleep and my mind starts to drift off but my heart feels like it's beating hard. It's quite uncomfortable. It's not slowing down and relaxing... It almost feels like the way your heart beats over a part of your body that's hurting (it doesn't hurt) but it's uncomfortable when I'm comfortable and drifting. grr.