Judging from what he had seen beyond the wall and the words of Varamyr Sixskins about his talent, this looked like a very powerful form of warging, enhanced by his magic and control of his mind. Slipping into the minds of his dragons or Ghost temporarily seemed to merge their minds and senses while leaving his body vulnerable. He could in theory, split his mind via occlumency and maybe stay in control of both his body and his bonded animal. In practice, however, all he got was a headache. And while he was sleeping before as Jon Snow, he had subconsciously been warging into Ghost, thus thinking that he had wolf dreams.