I know this post is tagged with fibromyalgia, but have you look into a pot's diagnosis because that is a very common symptom of pots. As far as what I do for that with my pots, compression garments are really helpful (Right now I'm only using compression socks which are the most accessible, but there's also abdominal binders and other types of compression clothing) drinking a ton of water, and increasing your salt intake. Some people do this by taking a salt shot meaning just eating straight salt or just eating saltier snacks