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]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "self-abasement":
   abasement, altruism, comedown, commitment, consecration,
   debasement, dedication, deflation, descent, devotion, disgrace,
   disinterest, disinterestedness, dump, embarrassment, hangdog look,
   humbled pride, humiliation, humility, letdown, modesty,
   mortification, put-down, sacrifice, self-abnegation, self-denial,
   self-devotion, self-diminishment, self-effacement,
   self-forgetfulness, self-immolation, self-neglect,
   self-neglectfulness, self-renouncement, self-sacrifice,
   self-subjection, selflessness, setdown, shame, shamefacedness,
   shamefastness, unacquisitiveness, unpossessiveness,
   unselfishness