There is nothing to worry about, your child simply likes the floor, just spread baby/ play mat on the floor for him to sleep on.
Hope there is nothing biting him on the mattress of the bed, just check and if there is nothing, it may just be one of those things. Habits that will pass with time, perhaps the floor is cooler too so make sure the room is cool enough as well, and when he is deep in sleep, transfer him to bed