freak out

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb slang, intransitive To react (or cause to react) with extreme anger or fear to something to the extent that one loses one's composure or behaves irrationally; originally, to suffer an unexpected and severe bad reaction from the recreational use of a psychotropic - usually hallucinogenic - drug,
• verb slang, transitive To scare someone.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb lose one's nerve
• noun a wild delusion (especially one induced by a hallucinogenic drug)