Sometimes, if under of your house's floor is air, you will fall instead of landing on the floor. It is a /sethome glitch. Also, if the house is set while building the floor, then this is more likely. The reason for this glitch is, the /sethome command tries to land the players on the best available y coordinates(searches only 4-5 blocks up and down where you /sethome i believe) and if the y(where you sethome) is occupied by a block(can be the floor by an odd glitch) and there is a 2 block high roof, then you will spawn in the middle of the air. The best is to fill under the floor with blocks, that way this glitch won't happen.