Speaking of side-effects of medications...
A few years ago, my brother-in-law was having very frequent severe headaches. It turned out that the cause was him overdoing his paracetamol intake for what had been less frequent, less severe headaches!!
I had exactly that
I got a sudden very severe headache - basically like someone hit my head from the inside with a large hammer
didn;t go away for ages
I went to A&E - on the insistance of the GP - and was told to take alternating ibuprofen and paracetamol and come back immediately if it got worse
they also did a scan and all that and found nothing out of the usual
anyway - it got a bit better with the pain killers but was still bad - and got a lot worse when getting close to time to take the next dose
I kept a very accurate record of what I took and the exact time to make sure I didn't overdoes
this went on for weeks - never properly went away at all
eventually I started wondering and decided to just stop and see what happened
it all went away totally
after probably 7-8 weeks
at some point the original headache (possibly a migraine) had gone away and been replaced by an identical one induced by the pain killers
worth people knowing about as it can happen to anyone