For years I've noticed that I find standing still more tiring than walking, even though I can walk very little, and that I have to sit with my feet up as much as possible because it's tiring when they're on the ground. This weird observation is common with CFS, but I didn't connect it with any of the "orthostatic stuff" - orthostatic intolerance, postural orthostatic tachycardia syndrome (POTS), or neurally mediated hypotension (NMH) because I don't feel dizzy or lightheaded when I stand up from sitting; or indeed, however long I stand. However, I read that difficulty standing for long is strongly suggestive of OI and that these other symptoms aren't always present so I did Dr Bell's "poor man's tilt test" (you take your heart rate at intervals first supine then standing for up to 30 minutes) and if your rate increases by over about 30 beats/minute, it indicates OI (POTS and NHM are subsets of OI). My heart rate went up 30 bpm so I went to my doctor for proper blood pressure measurements as well as accurate heart rate measurements while repeating the test and I got the diagnosis confirmed. I've been posting alot about OI in the last week and quite a few other people also said that they had no idea that they had OI until they got tested, again because they don't feel dizzy on standing and misunderstood about this being a major or even necessary symptom. OI is partly treatable! This is why it's important to get yourself tested if you suspect (from your difficulty standing for long) that you might have it. Treatments include raising the head of your bed, increasing your salt and water intake (under medical supervision), wearing medically prescribed compression tights, eating small, frequent meals rather than a few large ones, doing certain strengthening exercise to get your blood to where it needs to be, etc. There are also drug interventions as a next stage. Cort, as always, has produced an excellent information page on it. OI is basically about the body's failure to apply the mechanisms to keep your blood volume from shifting down into your legs and abdomen due to gravity when you stand. Astronauts get this when they come home from space and there is lots of research on it. There's a huge overlap with CFS - on it's own, OI is severely disabling and causes exercise intolerance. One estimate I read talked about 66% of CFS patients having OI, so I think it's worth us doing the test! I'm all excited about having identifed a potentially treatable (though not curable) part of my CFS and am looking forward to trying the various interventions over the next few weeks. I'd like to encourage everyone to consider testing - I'm beginning to think it should be done as standard when we're diagnosed.