Constantine Hering (1800-1880) was the Father of American Homeopathy and first president of the AIH (American Institute of Homeopathy). In 1835, with a number of other homeopaths, he established the Hahnemann Medical College in Philadelphia. Hering's rule of cure states that "During homeopathic treatment of a disease, symptoms disappear in an orderly manner. That is, symptoms improve from above downwards, from vital to less vital organs, from the most recent to earliest symptoms and the symptoms disappear in reverse order to their appearance."
(Homeopathic Dictionary, Jay Yasgur, 2004)
See if you notice this kind of thing happening in you or those around you. Some people call it a law, but there are exceptions, and so the word rule is more apt.
For further information and a comprehensive article see Herig's Law: Law, Rule or Dogma by Andre Saine, D.C., N.D. F.C.A.H.