According to an article I read a long time ago. It said Edgar Cayce
suggest applying castor oil to one side of a folded cloth and place it against the back of the neck.
It suggested using folded flannel cloth with a folded towel behind it to keep the castor oil from bleeding through the other side and staining the bed or back of the chair where you rest your head. I would think a piece of plastic would be better behind the folded towel would help?
The bio-cranial neck stretch exercises has helped many people with your problem.