Trying to fall asleep. 10 min of palpitations w/ fast heart rate. no other symptoms. doc says heart ok. can anxiety really appear in while relaxed?

Yes: In fact, people can have panic attacks in their sleep. What you are describing is pretty much the definition of a panic attack. Short period of time, intense, physiologic response w/o real medical probs. What were you thinking about at the time? Pas are very treatable with therapy, where you work to find your triggers and retrain your brain. I do not recommend just medicating them, tho meds help.