i'm so sorry you had to go through something like that.
i am new to POTS so, honestly i don't know what advice i could give you.
it's easier said than done but try to relax, and by all means don't exhaust yourself. I used to be bothered by the smallest speck of dust in the house, but right now i figure that my health and well being have to come first.
One trick that I've read about to lower your heart rate is to drink as fast as you can 2 glasses of water. Also, your beta blocker should help along with deep breathing.
From what I've read online, a heart rate of 200 + is not uncommon, but I guess everyone is different, so don't take what I'm saying for a fact.
try to talk to your doctor, i'm sure he/she'll be able to shed more light onto this.
Best of luck.
Alex
Yes, from your description of your activities, I would definitely say you were overexerted and under-rested. Rest and trying your best to keep to a routine schedule are extremely helpful in regulating the symptoms of dysautonomia, and deviance from this (i.e. overdoing it) can often lead to "flare ups" of symptoms which can last anywhere from hours to weeks. We all know that life can get in the way sometimes, though, and flare ups are an inevitable part of this for all of us, unfortunately.
A heart rate in excess of 200 bpm is not unheard of, and especially if it is alleviated by lying down, it's likely not something to be imminently concerned about unless your doctor tells you otherwise. Of course, when this happens, it is recommended to lie down to alleviate the cardiovascular stress that is causing the heart to react with such a high heart rate; if the heart rate fails to continue to be compensatory, loss of consciousness is the predicted outcome and the sharp increase in heartrate above what is usual for your POTS is your body's "hail mary" pass at compensation (to borrow a metaphor from football).
Loading up on fluids and rest should help, and is a good idea when flare-ups like this occur. Sorry you had this scare!
I'm going through the same thing. I go to the Mayo Clinic in Rochester MN and the only thing that has helped me other than taking my medicine is drinking three or four liters of water a day and increasing my sodium levels. POTS is really hard to deal with and there's not much you can do except rest, drink fluids and eat salt. Good luck.
Be careful. Although everyone pretty much blows this off as normal for POTS, your heart's electricl system can misfire when your rate is this fast. (Heart attack) definitely tune into your body and prioritize. Stop activity and lay down before it gets this high. Obviously by definition of our syndrome if POTS is the reason, pulse will always slow down with laying down