Sign or symptom

What innocuous sign or symptom did you notice that turned out to be a serious medical issue?

Not climbing or hopping in her cage, but sit under it. I thought it was just that she was getting older, but looking back it was a sign. Then I saw her go to the left with her head non stop. To the left and back, like she was following something. I remembered from the other one I had who got head tilt. I still had saved the meds. Her eyes started to roll uncontrollably too. Gave that 12 euro anti worm paste for cats. It got less. 5 hours later 2nd dose. 6 hours later it was just normal again. It was e cuniculi. I have to keep giving that stuff twice a day for 6 weeks at least.

I had a white spot under my tongue and I thought it was from rubbing against my tooth. It grew and the dentists said to keep an eye on it and eventually it turned into cancer.