Hi TaraElizabeth,
I can empathize with what you're going through. I'll see if I can add anything to the great advice you're already giving. I have dealt with some panic but heavy agoraphobia on and off in my life, starting at age 16. It comes and goes depending on my life situation. I did not take my first flight until I was 37. The first time I tried, I chickened out when the door got closed, and I insisted they let me off! I was so disappointed in myself that I vowed not to do that again. Less than a year later, I was given a chance to fly, by myself (taking two planes) to spend time with my fiance as he performed in a major city. It was a big deal, so I was determined to do this.. no matter what. What really helped me do this was focusing on the reward of going, not the going itself. I knew that this was an amazing event, and he'd promised to buy me any evening gown I wanted if I just showed up at the airport on the other side. He even had bets with friends that I wouldn't do it. By focusing on what was on the other side, AND reminding myself that I should not confuse excitement with panic, I made it. I was pretty nervous and panicked for sure, but I did it.
One of the things that has helped me through all of this is the growing realization that I am only cheating myself out of these great experiences when I refuse to try something. I found that when I HAVE to do something (like go to the grocery store when my husband is sick) or shop for food when everyone is out of town, then I find I can do it. That really works for me, also lately when I a feeling anxious in a store, I tell myself.. "hey I WANT to do this! And I'm enjoying it!" The other night my husband and I went to a housewares store. Now, I don't go shopping very much... and he's so used to me wanting to get out fast, that when I made a joke of "get me out of here fast!" because there was so much great stuff, he took me literally and was trying to hustle me out of the store! I had to explain that I was enjoying myself for a change. It's all mindset, and feeling that I deserve to shop in nice stores, and for you.. that you deserve to be happy and have this great vacation.
You mentioned you flew before, but you were medicated, and you felt anxious the whole way. You know what? You made it!! You arrived at your destination, and you didn't die, you didn't cause an incident on the plane, you achieved what you wanted to achieve!! Think about that.. who cares how you got there, you got there. You were successful and you can do this again. Like me, you tend to pre-live things. You mentioned having a nervous breakdown over this. I can relate, I did that once over a trip to see Elvis Costello (we even had backstage passes) I was so angry with myself for that, I vowed to stop avoiding things I'd regret later.
My advice is in those paragraphs. Do this for you.. you deserve a great vacation. If you get there "messy" so to speak, big deal, you'll be there either way! Use the next few days visualizing the wonderful time you'll have... take care.