Yesterday, I had to run an urgent errand about 6 blocks away. With all the rest stops required, it took me half an hour to walk home (it should be about a 10-minute walk for a healthy person). The receipt shows I left there at 11:51; it was 12:22 when I fell onto the bed. I barely made it up the front stairs ... I was feeling light-headed when I started, and by the time I got to the top step, I was on the verge of fainting. I had to put my head down for a while before I could get the key into the lock so I could get into the house to lie down.
Then I had to lie down for over an hour before I had it in me to go to the kitchen (a mere 12 steps away) to make a sandwich for lunch. The couple minutes I was standing in the kitchen was enough to make me feel faint again. (Fortunately, I had a pre-made salad for dinner, so all I had to do was grab that out of the fridge, didn’t have to stand up to do any prep work.)
Here we are more than 24 hours later, and I’m still having nausea/vomiting/diarrhea (which usually signals I’ve over-exerted). I feel like I’m running about a 101 fever, but the digital thermometer says 97.6 (a sensation described by many CFS patients as a result of autonomic dysregulation). If I sit up, I get light-headed; I had to do my work yesterday lying down so that I wouldn’t pass out while doing it. Just walking the dozen steps to the kitchen this afternoon to get something cold to drink was problematic; I skipped lunch because breakfast didn’t stay down.
It’s called "post-exertional malaise" and it’s one of the ways to differentiate CFS from psychiatric problems – psych patients don’t describe the same problems after exercising. You can call the complaints of being light-headed "subjective" and "not credible", but the next step into fainting is an objective sign that can’t be disputed, and I’ve done that many times. (Unfortunately, not in front of the doctors and judges who insist that they cannot believe anything they don’t see with their own eyes.) The vomiting and diarrhea are also objective symptoms that can't be disputed.
Researchers have demonstrated objective biochemical reasons for feeling terrible after exercise.
You could write these symptoms off to "the flu", but then you would have to accept the illogic that I catch "the flu" dozens of times a year.
In the years before I finally convinced a doctor to give me proper medication, I would feel like this after walking to the store inthe next block; mind you, as I was slipping into this relapse, I was walking 4-5 miles every day, so it wasn’t a result of a lifetime of being a couch potato. One week I could walk the two miles to work no problem, the next week it was a big problem, and the week after that I couldn’t manage it at all and had to switch to taking the bus.
It is absolutely impossible to write it off to "being deconditioned" when someone deteriorates that quickly, yet that’s exactly what some doctors try to do. (They claim to know the patient’s exercise habits better than she does. It "doesn’t make sense" so they turn it around in their head till they can create plausible reasons to explain why a 29-year-old woman of appropriate weight cannot walk more than a few feet without collapsing. Then they tell her what her history "should be" in order to support the doctor’s version, and get annoyed when the patient persists in telling the same story as before about previously spending weekends hiking in the nearby mountains instead of agreeing that the doctor’s theory is right, she spent all her free time watching TV and hates to exercise.)