My false percs do it all the time, one of them just lays on top of ot sometimes. Don't hate me, but when he(1") was intoduced my tomato clown(3") almost killed him, so I am wondering if he likes the vibration or if like a boxer he has become shot. He was introduced along time ago, before I knew how bad tomatoes could be, but he didn't bother the first perc. Is my fish just enjoying the vibrations or is he hurt? He will get up and swim around like nothings wrong. He also likes to swim in front of the powerhead more, and has not grown compared to the other one.(maybe he has became a she)