The shower issue is very common in CFS. I had this issue since CFS and POIs simultaneous sudden onset 30 plus years ago. I get very fatigued after I dry myself. That is very interesting that others noticed that too. Because the fatigue starts a few minutes after drying. But I can take long room temp (on the cooler side) showers and the fatigue does not kick in until after I dry. If I get into a lake, same thing. After I dry up I have to lay down. Note that a lake does not have force. Each time after i come out I have to lie down for 10 min if I have dried. Not if I don’t and go back in while very wet. So keeping wet while at the lake as much as possible minimizes multiple bath reaction. I do not have an explanation as to why it may happen after I dry.
I use very mild soap. Otherwise it is murder.
My speculations as to why this maybe happening is that our skin may not be working well, our CNS also. My skin is dry most of the time. Skin being a connective tissue and not working well may leak stuff in. Maybe for the same reasons our tubes may leak at ejaculation. Maybe leaky skin and connective tissues is causing an inflammatory reaction for the immune system to clean up what is leaked.
I lay down for 10 to 15 minutes after a shower and a good portion of the fatigue goes away. I think my CNS also needs to adjust. It feels like my blood is not getting where it should and it is so much work to do anything if I do not lay down first. Again 15 min laying down right after drying up helps me recover significantly, but not 100%. I noticed that if I take Vit D2 BEFORE (at least 20 min before) the shower or bath after-effect is greatly decreased. Note that D2 is anti inflammatory, but also it makes CNS work better, helps hormones, etc. if I take too much, it is excitatory. So I take 1000 mg of D2 only. I do not tolerate D3. It too excitatory for me. A common name for D2 is Ergocalciferol. i get it from Amazon in drops, about 17 US$ per bottle. I take 5 drops, that is enough for the day. And it improves my cognition and energy also. I reduce D2 in day 2 after O because it can make that hard day worse sometimes.
So why does it wait after drying up? What a mystery. I think the whole thing is partially related to not getting the skin well irrigated due to poor perfusion, and our bodies eating up needed (by connective tissues) amino acids to burn them for energy. I think after O my body desperately needs amino acids to compensate for an impaired glycolysis pathway. The impairment being greater after O.