regarding your headache diagnosis. If you just ask: could my headache be a brain tumor, the answer is probably: very unlikely but it might be. thats because its actually true. there is actually a non 0 chance that headache is a symptom of a brain tumor. From a bayesian standpoint though its really super super unlikely, especially if there are no other symptoms that might shift the prior.

a better way to use an LLM here is to let it research scientific papers (or medical guidelines) on headaches. then give it as much info on your symptoms as possible, and then ask it do deduct potential diagnoses. You can even ask it to calculate probabilities if thats what calms you down. Probabilities based on studies and available information. IMHO, this always leads to a more rational response.

maybe you are doing this already, idk. just wanted to share what works for me.