There has been quite a bit of discussion lately on various blogs regarding POTS and OI. I'm still learning about this and upon reading the description that Sue sent me I have probably had this condition since I was in college almost 30 years ago. I still remember almost passing out one day when I went from sitting to standing. It was damn scary. My vision got all black around the edges and I had to sit back down fast before I fell down. More recently I've had trouble at work when sitting at the computer for long periods of time. I'll get lightheaded when I get up to move around. Someone told me to eat something salty and that worked quite well. However, I still had trouble when paired with an office mate that like the heat turned up. I would actually get nauseous as well as lightheaded. I would have to take my work to another location so I wouldn't become physically ill and all this happened before I had CFS.
Of course at the time I had no idea what was wrong with me. I knew that heat didn't agree with me and I had to have a cooler office than most people liked. The one time I went to a doctor about it when I was in college I was told that there was nothing wrong with me and that I just wanted some attention so I never went back to a doctor for these symptoms although they bothered me for the next 25+ years. Of course I wasn't helping myself since I have been eating healthy all those years and hence had cut almost all salt out of my cooking. It turns out that I should have been adding it. Anyway, here are some useful links regarding POTS and OI. Let me know if you have found any others in your internet travels.
Ten Tips from CFIDS.org
About OI from CFIDS.org
Meds for OI from CFIDS.org
National Dysautonomia Research Foundation
Sue's blog article