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
Jimmy'll come in off the road, you won't be there, he'll freak out and call you a hundred thousand times.
If someone freaks out, or if something freaks them out, they suddenly feel extremely surprised, upset, angry, or confused. I remember the first time I went onstage. I freaked out completely I think our music freaks people out sometimes It sort of frightens me. I guess I am kind of freaked out by it