Yes that happened to me too except this happened after a 50% water change. The fish started to dart fast went up then down darted some more then bellied up. Then the next time I changed the water another TF did the same thing. I think what happens for some reason they go into shock. I thought maybe it was the chlorine remover I never used before. I never had that happen before. Since then it hasn't happened again. I had them 6 years so I was disappointed. I have only one of the oringinal 3. I have had him now 8 years.View attachment 250250