>>1
You sure it's out of the blue? If you look at your life, maybe there are obvious stressors that are causing it? Anxiety is a normal human emotion, not a disease. (But of course it's not normal to have anxiety all the time, in the absence of any unusual stressors.)
Look at food. Are you eating any crap with preservatives, additives or artificial sweeteners?
Many years ago I discovered that soft drinks with aspartame and acesulphame-k gave me a panic attack. It was 100% reproducible. Quaff diet drink, wait 20 minutes, freak out. I was not a regular drinker of these, just trying them out and I never, ever had panic attacks before or since.
Cut out all junk, and try to solve the stress-inducing problems in your life; see if it goes away.