I just got a new Betta two weeks ago after my previous one died (he was old).
I keep a thermometer in my 1 gallon aquarium which is attached to the side with a suction cup. My new betta is obsessed with it. I removed it for a short period today to test the water temperature in the tank I place her in while cleaning the big tank. Immediately she started twitching and convulsing throughout the tank. I put the thermometer back and she is just fine.
There are no other behavioral differences and she eats normally. She likes to stare at the thermometer for large periods of time but does occasionally swim away.
Is she sick or just is she just getting upset that I removed something to which she is attached, from the tank?