The Collaborative International Dictionary of English v.0.48:

Self-abasement \Self`-a*base"ment\, n.
   1. Degradation of one's self by one's own act.
      [1913 Webster]

   2. Humiliation or abasement proceeding from consciousness of
      inferiority, guilt, or shame.
      [1913 Webster]

WordNet (r) 3.0 (2006):

self-abasement
    n 1: voluntary self-punishment in order to atone for some
         wrongdoing [syn: penance, self-mortification, self-
         abasement]