It turns out this is called "Somatic Symptom Disorder" (SSD):
https://www.mayoclinic.org/diseases-conditions/somatic-symptom-disorder/symptoms-causes/syc-20377776
From other sources, it appears that this is especially common in people newly-diagnosed with cancer, and it's tricky for healthcare providers because sometimes our aches and pains do genuinely mean something. According to the Mayo page linked above, here are some of the key warning signs that we *might* have progressed from normal self-monitoring to dysfunctional SSD:

- Constant worry about potential illness
- Viewing normal physical sensations as a sign of severe physical illness
- Fearing that symptoms are serious, even when there is no evidence
- Thinking that physical sensations are threatening or harmful
- Feeling that medical evaluation and treatment have not been adequate
- Fearing that physical activity may cause damage to your body
- Repeatedly checking your body for abnormalities
- Frequent health care visits that don't relieve your concerns or that make them worse
- Being unresponsive to medical treatment or unusually sensitive to medication side effects
- Having a more severe impairment than is usually expected from a medical condition

I hit a number of these during the first year after my diagnosis. I think it calmed down for me once I'd had time to establish what a new "normal" baseline felt like after the nerve damage from my spinal metastasis, and the normal pains of regaining mobility after a few months in a hospital bed. The Mayo page suggested seeking treatment early, or else there's a risk that you can get "stuck" in this.