Betta fish odd behaviour

Question
Hello :)
My one fish, a blue betta male, has been acting odd for a few days, and I'm getting slightly worried. He is constantly in one of the corners of his tank with his nose at the surface, his body vertically down, and every few minutes is thrashing around a bit, as if trying to jump out of his tank. He hasn't been paying much attention to his food the past two days, either.. I just don't know what to do, he was a little more lively before I put him in that tank, but before that, in his other tank, he was fine. :(

Answer
Sounds like a type of metallic poisoning or environmental shock. Hell either come through it or unfortunately die. The only thing you can do now is to try to gradually mimic the same conditions you had in the other tank so that his body comes out of shock. Best wishes
Alexander