Can you post a picture and or short 20 second video of the fish swimming funny?
Have you added any new fish to the tank in the last 2 weeks?
Have you checked the water quality for ammonia, nitrite, nitrate, pH and GH?
If yes, what were the results in numbers?
How often do you do water changes and how much do you change?
Do you dechlorinate the water before it is added to the tank?