I've been struggling for a few years with this, I think it's got worse since covid (when my physical fitness left and I've struggled to get it back).
After doing ANYTHING that's not sitting around, I get completely exhausted - not at the time but once I stop. I also get really stiff (even if just standing around) & struggle to take off shoes/socks & struggle to move/get up once I've sat down.
I don't know if it's a fitness thing as I'm fine while I'm up and about, just afterwards my body seems to seize up!
Anyone have similar/any advice?