also sorry i f i have said this before - foggy today
but how you kow any post effects are from the exertion or from other upright time ... eg walking round the house, getting your pill s out ( 30 mins) sitting up reading etc.... unless you monitor it or stay ndown all the time you cannot really tell what causes what IMO
just being upright doing mundane things will make me ill
the more I stay lying down the better
but to compare the two you would eed to hav ethe much desired servant for a week or two
would be agood research experiment - also to help differentiate PEM from crashes..
A
I agree with what others have said in that what you've labeled as a "crash" sounds very much like an OI attack. It comes on within a fairly short time of being upright, I get dopy-headed, feel unwell, sometimes I can tell my heart is going too fast, eventually I get a little spacey or dizzy, etc., but lying down or drinking electrolytes, etc. can resolve those symptoms fairly quickly.
A "crash" as I would define it is PEM - it hits the following day, and I feel like I've been run over by a truck several times and caught the flu. Or if I'm lucky and it's milder, I just feel generally like crap and like I'm getting a cold. It lasts for a day or more, depending on how badly I've overdone it and how good I am about resting fully to recover.
If being upright makes you feel ill and if you lie down for a while it gets better, that's OI. If being upright wears you out and then the following day you can't stand up to get to the bathroom and everything hurts and your body feels like it's imploding, that's PEM. Note that the first one can lead to the second. Walking around with orthostatic intolerance issues is a big strain on the body, and uses up a lot of energy.
The difference is pretty distinct for me. I don't ever get OI symptoms when I'm lying down. But if I overdo it with activity while lying down, I will get PEM. I've been pretty much bed ridden for the last two years, so there have been plenty of times where I've been lying down only, and I can tell you with confidence that it's still possible to trigger PEM.