I am a 37 year old male with no medical history. At night…

Good evening. My name is***** one of the JA experts. For one, I believe there is nothing serious going on. Your presentation can be explained by the fact that when you're sleeping at night your nervous system is dominated by the vagus nerve. It's well known to "slow things down" in your body which is normal for relaxation. So, your heartbeat gets slowed down vs. when you're active during the day. Your blood pressure normally goes down as there is no need to pump more blood than what's required just to maintain basic metabolism. So, at 3 a.m. you wake up (which is not usual in and of itself. People don't typically need to do so). Likely you're waking up from so called deep sleep when your body is quite relaxed to go to the bathroom. Guess what - all of a sudden you need your blood pressure up but when you get out of bed being relaxed it actually doesn't get up but in fact goes down and more so if you do it suddenly and not fluently. It's called orthostatic hypotension. So, your blood pressure went down when you actually need it up. So, your heart reciprocally gets turned on to pump more blood to maintain your blood pressure and and when it does so, it does so at the expense of increased heart rate as it can't hold more blood than it normally can, so it has to compensate the higher demand by increase in heart rate. That's "that simple" from the physiology stand point!