Anxiety and panic attacks can sometimes have very seemingly unlikely causes. In fact, there are studies which clearly demonstrate that virtually all such cases have some kind of a "hidden trigger".
As a matter of fact, if the trigger isn't deeply hidden, it is rare for this to be a case of a "classic" anxiety/panic attack.
Occasionally this is a straightforward link, e.g. you get exposed to a highly undesirable situation and then you "automatically" fear anything that reminds you of it and have a panic attack when faced with something like that. These cases are relatively easy to "cure" because the afflicted person has the the whole causal picture he/she can unravel with a little time and patience and rational analysis.
But the vast majority of anxiety/panic attack cases have deeply hidden triggers, sometimes going back years. And those triggers don't even have to be "direct" in any "rational" sense of the word.
In those cases a good psychotherapy (especially clinical hypnosis) maybe the best, if not the only, way to deal with it. I know someone who has tried something called the "Dreamwalk Therapy" available online and - has beaten this thing in a matter of days - as incredible as this sounds.
The "trick" appears to be to gain access to that "primary" cause, and that's why hypnotic relaxation, guided by an experienced therapist, can be the very thing that releases that memory and allows the patient to rationally deal with it.
But under all circumstances, you should be extremely wary of taking psycho-active drugs for this. Just say no!