Been having palpitations. Have had anxiety and panic attacks in the past but am currently not stressed or anxious. it just feels like a fluttering and can last a couple of hours at a time. I do not have pain or breathlessness. I find it sometimes happens as I am dropping off to sleep an wakes me suddenly as if I have temporarily stopped breathing . I have a device in which to take my pulse which seems to be unaffected by these episodes. Just want to know if it is anything to be concerned about?