Ye I've had this too, not a nice feeling and worrying, I have had checks all fine but that doesn't put my mind at rest. It happens to me during the day out of the blue feel a flutter then heart races I find myself watching TV relaxing and checking my pulse! My husband hasan app on his phone and I hate when he uses it cause he's a runner and got low heart rate about 45 and mines is about 75 relaxing and shoots up the minute I move. Adrenalin / anxiety must have a lot to do with it I'm jumpy where as my husband is so laid back, nothing bothers him. Hope you feel better soon and find a way to cope with it
X