iniscent of threat or trauma. The individual is placed on high alert in order to be certain
danger is not near. Hypervigil ance can lead to a variety of  obsessive behavior patterns, as
well as producing difficulties with social interaction and relationships.
hypomania An abnormality of mood resembling mania but of lesser intensity. See also
MANIA .
hypopnea Episodes of overly shallow breathing or  an abnormally low respiratory rate.
ideas of reference The feeling that causal incidents and external events have a particu-
lar and unusual meaning that is specific to th e person. An idea of reference is to be dis-
tinguished from a DELUSION  OF REFERENCE , in which there is a belief that is held with
delusional conviction.
identity Experience of oneself as unique, with cl ear boundaries betwee n self and others;
stability of self-esteem and accu racy of self-appraisal; capaci ty for, and ability to regu-
late, a range of emotional experience.
illusion A misperception or misinterpr etation of a real external stimulus, such as hear-
ing the rustling of leaves as the sound of voices. See also  HALLUCINATION .
impulsivity Acting on the spur of the moment in response to immediate stimuli; acting
on a momentary basis without a plan or consid eration of outcomes; difficulty establish-
ing and following plans; a sense of urgenc y and self-harming behavior under emotion-
al distress. Impulsivity is a facet of the broad personality trait domain D ISINHIBITION .
incoherence Speech or thinking that is essentially incomprehensible to others because
word or phrases are joined together without a logical or  meaningful connection. This
disturbance occurs within clauses, in contrast to dera ilment, in which the disturbance