I have been waking up with tachycardia on a nearly daily basis for some time now, and I m wondering what this could possibly be. It never occurs while I m awake, and when asleep always occurs during REM sleep. I don t think it s apnea and I don t see how it could be anxiety as I don t feel anxious *until* I m awakened by the palpitations, and the dreams from which I m roused are not particularly unpleasant or stressful. (In fact I ve never had what I would call a nightmare in my entire life.) When I say tachycardia, I mean a heart rate of 110-120, but sometimes my pulse is only around 100 but my heart is nonetheless beating sufficiently *hard* to have awakened me. This always subsides within ten minutes of waking. What are some possible causes? Thanks.