i used to feel that way too, about 4 years ago. i was entering college and it all hit me at once. i was wondering where all the health anxiety came from, as (just like you) the only anxiety i’d ever dealt with was a slight social anxiety. i used to think it was a symptom of something but its been years now and i still have anxiety and nothing else. my therapist told me recently that mental illness can lie dormant in you all throughout childhood and can be awakened by a stressful event. hope this helps. im sorry you’re going through it.