Green’s Dictionary of Slang

freak v.3

[abbr. freak out v.]
[1960s+] (orig. drugs/hippie)

1. to lose psychological control, whether enjoyably or otherwise, as the result of drugs, usu. hallucinogens; usu. as freaking.

2. (also freak one’s mind) to worry someone, to disturb, to cause severe anxiety (the extent of the disturbance varies totally as to context) (cf. freak out v. (2)).

3. to worry, to be worried, to be severely anxious.

4. to act in an emotional, melodramatic manner; thus freaked adj., emotionally overwhelmed.

5. (US gay) to be uninhibited, esp. at a party.

6. (US black) to perform.

In compounds

freak attack (n.)

[1990s+] (US teen) a state of extreme tension.