could be a few things, need to know the parameters for the spell. you could of just had dragons on your mind and it spilled over to your dreams. you maybe you were projecting. sometimes people project without knowing.
that being said however, you cannot create a dragon. in that sense, i don't think it's a real spell, but maybe the dream is showing you something, it could be showing you your future dragon guardian, or maybe into the past. i'd do some dream interpretation and then work on some astral projection. look into Dragon Magick but keep in mind it's not for everyone.