well its sounds like your poor fella has swim bladder.
basically there reason swimbladder is caused is because if he is being feed falke food, he is swimming upto the top of the tank getting a mouthfull food but also taking in a lot of air aswell. So tis just basically blocks up the gills and gives them inability of not being able to constanly swim. With swimbladder you find him floating at the top of the aquariam
or at the bottom. It is not really curebale but there are many diffeent methods you can do to help him.You can feed frozen peas some frozen frozen or salt tonic

I agree that it could be swim bladder but I have two lionheads that like to turn sideways and scratch their sides on the gravel at the bottom of the tank. They don't lay there for long periods so don't know if this is related but worth chiming in on.