Heart Pounding

I have had the same experience. Wrote down my elevated pulse numbers and took them to my doc. Long story short -- many tests -over 16 month period - now on BIPAP machine and oxygen. I have an appointment with a recommended cardiologist. Hoping to have another heart monitor to see if any of this is really helping as the "cures" interfere with my good sleep a lot.
Good luck on your search for a remedy.

@dalebout123 thank you for sharing. I assume you have sleep apnea.

When sleep is interrupted, including when rising to urinate, or when just awakening normally each morning, cortisol levels have risen automatically as part of the process. That's a stress hormone. Also, glucose levels rise in sympathetic response to your beginning to awaken and maybe have to flee or fight...also a stress response. This invites adrenaline rise in the blood, also a stress response. If you awaken mostly due to high CO2 levels in your blood (we don't breathe because our oxygen is low, we breathe because CO2 levels in the blood are too high...yes, it's true!), it might be due to sleep apnea, although sleep apnea runs 'all night long.' It would be unusual for a person to routinely awaken, pounding heart or not, near 0300 each and every night due to sleep apnea as that problem persists for as long as you are asleep. In fact, the apnea-hypopnea index that CPAP machines give their owners each morning is a calculation of all such events over each hour of sleep. My untreated AHI was 31 events per hour (!!!!!), or just into the 'severe obstructive sleep apnea' category. Well, if I have even six events per hour, and not a whopping 31, wouldn't one of those six lead to the pounding heart problem? I would think so.

So, this might be sleep apnea, and it should be investigated, or it might be a Vagus nerve/parasympathetic system dysfunction, or it might be paroxysmal SVT or AF (supraventricular tachycardia or atrial fibrillation) that is self-limiting...and I suspect you eventually fall back asleep if you aren't wide awake and in some fright or concern.. Either way we look at it, you DO appear to have a self-limiting tachyarrhythmia, and it needs to be seen by a cardiologist. The cause at this point is indeterminate; it might well be obstructive sleep apnea, or temporary central apnea (brains 'forgets' to cause you to breathe, oddly because you sometimes over-flush your blood with oxygen, your CO2 falls very low, and your brain gets fooled into complacency...for want of a better explanation. An over night polysomnography in a sleep labe will soon show you if you need PAP therapy of a kind. There are several different forms of PAP therapy, and most patients can only use one, at most two, well enough to be deemed 'treated.'

@gloaming thank you for your detailed response. This is very helpful information that AI could never do. I really appreciate your time.

@zubedude
I have apnea and sometimes I wake to my heart racing, head throbbing and high BP. I would consider an overnight sleep study...