A real fun one is rebound headaches. Spent a few months with horrifically painful headaches. Turned out it mostly from painkillers. More I took. Worse headaches Got.

My other less painful headaches that started the cycle were an actual brain issue. Just took a few years to get correct diagnosis.

Eventually had a cycle of one round of pain killers every other day. Cycling through To a different kind each time. This mostly worked until I got excess brain fluid drained off. Which actually solved issue.