What Causes Heart Palpitations While Arising After Sleep?

When I lay down to rest for a 20 min nap, I will come out of sleep so to speak with what seem to me an elevated heart rate. A bit of panic comes over me. When I sit up, take a few breathes, it seems to be fine. It s most noticeable and more frequent when I have stress going on in my life. I do drink coffee as well, daily. Is this something serious? YYYY@YYYY