This is a good point.

There is a feedback loop to anxiety and stress and illness.

Some illnesses cause minor problems for decades, but you remain mostly fine.

Add in a huge dose of stress hormones, and that minor condition can go crazy. You now have more things to stress about.

Inflammation can cause inflammation. Sometimes breaking the cycle is enough.

The brain is just another organ, and also vulnerable to inflammation and immune effects. And it can in turn cause or worsen them too in the rest of the body. Medicine truly must stop making psychiatric diagnoses without looking for systemic causes, and vice versa. And I think good doctors understand this. However, like any profession, there are plenty of not so good doctors who lazily throw people away with vague anxiety or pain syndrome diagnoses.