I think this one is very possible. One of the factors could be a diet itself, something that we may not be able to tolerate and it gets worse after we continue to eat it. I think the influence of a diet is still hugely underrated, a wrong diet could easily cause all of the other things that were mentioned here, autoimmune conditions, inflammation, then infections and eventually mitochondrial damage.- an enzyme, somewhere, is blocked or has lost affinity with a co-factor which can no longer help. Metabolic issue. Not making food into energy, which overtime, becomes worse and worse.
Currently on B12 transdermal oils (about 3 months), tried the B1 megadose thing to no avail so far...
If we are in some type of a viscious cycle, it could be the case that anything we eat could make us worse, and then even fasting could make us worse, at least up to the moment when we fix that part. It may also be caused by a single macronutrient or ingredient, or a combination of them that we do not tolerate, just like in celiac disease or any other food sensitivity. This could explain sudden remissions and short term remissions, because we usually never eat the same way every day.