In reply to J1234: This might sound stupid.... but try a wall. Any wall about 4 foot high will do. just get used to doing the motion etc.
Trying a vdiff or severe with one "near the floor" is pretty pointless if your are trying to build confidence as you're near the floor anyway and unlikely to be phased.
Go find a wall very near to you, nail the whole rockover thing and then go back and nail the one you couldn't do.