The Collaborative International Dictionary of English v.0.48:

Freak \Freak\, v. i.
   1. to react with irrationality or extreme emotion; to lose
      one's composure; -- often used in the phrase

   freak out.
      [PJC]

   2. to become irrational or to experience hallucinations under
      the influence of drugs; -- often used in the phrase

   freak out.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Freak \Freak\, v. t.
   1. to cause (a person) react with great distress or extreme
      emotion; -- often used in the phrase

   freak out.
      [PJC]

WordNet (r) 3.0 (2006):

freak out
    n 1: a wild delusion (especially one induced by a hallucinogenic
         drug) [syn: disorientation, freak out]
    v 1: lose one's nerve; "When he saw the accident, he freaked
         out" [syn: freak out, freak, gross out]