yes, stress can kick a mild autoimmune issue into overload, and once there it can be almost self-sustaining.

what is physically happening is that the body's mast cells release neurotransmitters like histamine and serotonin, causing inflammation (so the immune system can fight some things off) leading to pain, and also fatigue (to encourage you to stay safe at home in the cave conserving energy, or some such story like that -- don't trust any specific just-so story though, especially this one).

the interesting question is what all the other things are that stress you out. i've found dietary triggers are what got me and a lot of my friends; there are some allergy cases out there, and a few friends with long COVID, which is one particularly nasty self-sustaining form. a family member had a terrible decade long episode triggered by contact dermatitis with poison oak. and generally speaking, heat and humidity are stressors too, as are pressure changes (you've heard tell of the little old lady who can tell a storm is coming because of an arthritis flare).