shower suggestion - use a portable seat or stool in the shower
Re: hot showers, I have NMH (Neurally Mediated Hypotension, a different type of Orthostatic Intolerance), not POTS, but showers are also hard for me. One thing that helps me is that
I don't stand up to take a shower. When I was really sick I could not stand up at all - too much dizziness and nausea. I had to sit down during my entire shower, sit down to dry off, etc. Now that I'm a bit better I can stand up for a short time just to get wet. Then I turn off the water (two advantages - shower stall not as hot and it saves water/energy!) and sit down to soap up or wash my hair. At the end I stand up to rinse off.
You would think that baths would be good (sitting down) but they are worse than showers for me. Being surrounded by warm water would be horrible for my NMH. Maybe they would be okay if the water was really cold, like a swimming pool? I'm not sure I'd like the idea of a cold bath!
So I guess I'll stick with my method of sitting down in the shower.
Our current shower stall is a fiberglass shell with built-in seat. But before we lived in this house I had a portable shower seat (it fits in a bathtub) that looked something like this -
http://www.amazon.com/Medline-MDS89745R-Shower-Chair/dp/B0007YX29A
You can buy seats like this in most drug stores (pharmacies) in the USA. I recommend getting a seat with a back so you can lean back when feeling tired. We also made sure to have a grab bar in the shower (bolted to the studs) so that I can grab it if I slip or have balance problems (those are not as bad as they used to be, thankfully).
I'm not sure if this is true for people with POTS but for me (with NMH) I find that
reducing or eliminating time standing still *for any task* is quite helpful. I sit down to brush my teeth, for example. I have a small stool in the bathroom, a higher bar stool in the kitchen to reach the counters, and so on.
I always wonder about those studies that measure "activity" because any ME/CFS patient like me, who has NMH, probably has a much harder time with standing still (which would seem to be a less strenuous activity according to activity monitors) than with a 5-6 minute walk (which I assume would be measured as a "more strenuous" activity). Standing still is the
worst thing I can do and I feel it the next day. The next worse thing is sitting still, straight up, without a back support (e.g., at the computer I forget to lean back), and with my legs hanging down (if I forget to bring them up in the chair and cross them).
Edited to add - I see that this got much longer than I originally intended, and is a bit of a digression from the original topic of stress/adrenaline as a trigger, but I hope it was helpful!