The Collaborative International Dictionary of English v.0.48:

Hypnogenic \Hyp`no*gen"ic\, a. [Gr. ? sleep + root of ? to be
   born.] (Physiol.)
   Relating to the production of hypnotic sleep; as, the
   so-called hypnogenic pressure points, pressure upon which is
   said to cause an attack of hypnotic sleep. --De Watteville.
   [1913 Webster]