When I first got sick, I was determined, as I am now, that I was not going to let POTS derail my life. In the beginning, this meant continuing to agree to almost all the things I could physically endure. It took months of low-grade fevers for me to realize that this was a HUGE mistake. Over time, I have learned which activities trigger my symptoms and I do my best to avoid them. This means saying no to hot summer picnics and long nights spent standing and drinking in bars, which can annoy people when you are a healthy looking 20-something.
At first, I felt guilty about saying no to things I was invited to, but eventually I came to realize that if I reduce my involvement in some types of activities, I am much more functional in other areas of my life. Saying “no” to a few things makes me able to say “yes” to the important things. This realization was a turning point in my struggle with POTS. It empowered me to say no to things without nearly as much guilt because I knew it was best for my long-term health. It has also been helpful that over time my friends have come to know the types of things I cannot do and they will no longer pester me about trying things we all know are bad for me. The other thing that happened is that I eventually learned to distance myself from the people in my life who thought that a night of drinking or an afternoon in the sun were worth the fevers and body aches I would have to endure later.
All this being said, saying "no" to things you would really enjoy doing is still a hard thing to do. In order to make myself feel better about times when I have to skip out on activities I used to love, I like to replace those activities with things I can do. For example, recently I had to back out of going to a summer concert because the record high temperatures meant there was no way I could go. Instead of just sitting at home thinking about how sad I was that I couldn't go to the concert, I went and got a massage instead. I find that if I structure these decisions as "trades" instead of just giving something up, it is much easier to tolerate them.