Why is my fish spinning?

  okay last night i had just bought him and he was fine and when i came to feed them this morning he was spinning like flipping Help hes salt water if that helps? and i already quarantined him so help? also i have two others and they ' re fine what should i do??
umm that happened to me once with a neon tetra its called wirling disease or hes just sick they do that when they get srtessed but quarintining him isnt gonna help its onlt gonna stress him out more so put him back and raise the water tempurature by 2 degg=ress and maybe hell get better eventually