My gecko's tail almost always drags.
Generally they only lift it when they're aggressive or striking food that I've found. She does... slither it though. When she walks she kind of slithers and her tail will follow that same sway.
Yeh, they dont keep their tails up all the time, they just let it flop on the ground and drag behind them haha.
If its dragging its bum then thats a problem.