I can relate - the exact way your anxiety begins is the same for me. I can feel an attack coming because suddenly I'll feel light headed, and detached. That's when I start mentally thinking "Oh crap, here we go again." Like you, I can also trace mine back to a specific day. 3/18/13. Prior to that, I hadn't had any major symptoms of anxiety but I do recall being stressed out from a busy holiday season at work, and having to deal with an unusually high maintenance/demanding girlfriend that I had broken up with that January. Kinda silly, I know, but without going into detail it was a pretty intense situation.
I've had to cancel get-togethers with friends, trips, going out, etc because of sudden anxiety problems. They can literally come from nowhere. My friends have been amazingly understanding and supportive through the whole ordeal. They're just as bewildered as I am, how this can suddenly happen to someone that was pretty grounded and laid back. We would go down the list of symptoms I had been having, and try to tie them to possible causes based on things I might've done that week, or anything that could be stressing me. Nothing ever stuck, I'd stop all caffeine intake, and still have attacks. I'd work out more, or less, and still have attacks. They even occurred while I was on vacation from work, and just sitting at home doing absolutely nothing. They weren't always constant, there were times I felt normal and could go out and enjoy myself. But every few days, the symptoms would come back. It's important for me to say that during this time, I was in absolute denial of the whole "anxiety" theory. Again, I thought I was too laid back and relaxed for that, and searched heavily for a biological reason. Visited several dr's, ER trips, imaging, etc. All came back normal and the only problem was what it did to my wallet in co-pays. Thankfully I'm insured.
When I finally accepted it was anxiety, the attacks became MUCH easier to deal with. Not fully 100% cured, but definitely on the right track now. That's how I ended up here. Seems like you're ahead of the game, and accepted it as anxiety from the start.
I've noticed that sitting down, taking deep breaths, and drinking water does seem to help alleviate some of the symptoms for me. When it gets real bad, I get as comfortable as possible (usually laying in bed with the lights off) and just ride it out. It's real hard when it happens at work, I just do the best I can to get through it and not let it impact my job. It's not easy at all though.