Do you have any stomach conditions? IBS, food allergies or sensetivities? I've been having the same situation for a few years, waking up with heart pounding, stomach cramped, sweating and dry mouth and was eventually diagnosed with IBS. I was told that when the stomach becomes irritated it can cause the intestines to lock up or seize, throwing me into the "fight or flight" mode, with me waking up not realizing what was happening. I started keeping a log of when and what I ate in the evenings until I figured out the foods that were triggering my episodes, red pepper, spinach, beans, etc. Once I stopped having the offending foods for dinner the episodes all but stopped. I still get them on occasion, but I've learned a few tecniques that help depending on the conditions. Drinking a glass of water or massaging the lower abdomen will sometimes kick start my digestive tract, but usually I turn onto my side and pull my knees to my chest until my stomach starts churning and making noise, the episode usually subsides pretty quickly after. I hope this info helps someone, because this used to scare the heck out of me.