my yellow tang's has started some strange behavior.....it has started dashing around in small bursts back and forwards with its fins all erect....its still eating as normal and everything else seems fine with him....he also swims backwards and does a sort of shaking thing back and forwards at the end of the tank....theres no white spot on him and hes not rubbing himself on the rocks or anything like that.....when i put food in hes still right up there eating away at spiritula or mysis shrimp.....im just worried theres something wrong with him cause hes been doing it for 2 days now.