My theory is this is related to either bacterial fermentation or some things not detoxed properly by the body (no metabolism in night and no movement/drinking) (e.g. uric acid from protein or dead bacteria or whatever)
So when taking a new supplement or food, I always try to have it in mornings instead.
Interesting, I still haven't recovered from the collagen even nearly a day later I will not take more atm because I have important things I need to do like my tax return which when I'm feeling normal I already feel overwhelmed by.
I have a few different types of brain fog that have a different feeling for each
for example :
Brain feels inflamed/ painful in the morning/ infection feeling in the brain this is oxidative stress for me : Sulforaphane with wasabi, NAC, arginine get rid of it for me
Then I have a more neurological brain fog feeling doesn't feel infected - this is from POIS, showers, high gi foods
Then excess histamine brain fog from high histamine foods, collagen this brain fog feeling is pretty similar if not the same to the neurological pois brain fog, i guess shower is histamine tbh.