If you know the reason for your anxiety then you can take steps to deal with it so the experience calms down or becomes obsolete, but if you do not know the reason then it can leave you somewhat high and dry with no clues as to how to deal with it.

I would argue that every phobia is simply a fear of feeling afraid. A phobic reaction has nothing to do with the trigger itself. It is a fear of the feeling that you get when that trigger is there.