I generally don't really get anxiety, but I've had some of the things on the list happen, and it never ruined our trips.
In September 2014, we were headed to WDW for a long weekend (just three days). Right when our plane was supposed to board, we got word that all traffic in and out of O'Hare was halted due to a fire that some idiot set at the radar center. We sat in the airport for 12 hours and never did get on a flight. We were going to cancel the whole trip, because there would really not be much point in flying all that way for one night.
We ended up calling WDW, work, the airline, etc., and we were able to push everything back one day. We got on a flight exactly 24 hours after we were supposed to leave, and we had a fantastic trip. Sure, it was stressful at the very beginning (especially when my older daughter burst into tears as the giant "CANCELLED" flashed on our gate screen), but we made it through, and it was actually kind of an interesting experience. We had a nice lunch at Macaroni Grill at the airport, the kids played at the play area, and then we went over to a gate for an afternoon flight where we were on standby. It turned out it was a Make a Wish flight, so they had cake, games, balloons, etc. Even though we didn't get on a flight, we had fun talking with the kids and the families and waving streamers and cheering, and we got more cake to eat than we needed

. My DDs both walked away with treats and balloons to take home, too. We bonded with other travelers who were missing cruises, work events, family weddings, etc., so our day delay for WDW didn't seem so bad.
Now, I don't wish for lengthy flight delays (I've been stuck at O'Hare for more than 12 hours on three separate trips, and it's not my idea of a great time), but I know that it's just a hurdle to overcome on the way to an awesome trip.
I've also been sick on trips before and had blisters. It's been ridiculously hot and crowded. We just try to be flexible. On one of the super-crowded days during our Thanksgiving trip, we bailed on the parks and spent the afternoon and evening exploring the deluxe resorts. It ended up being a really fun day. Just go with the flow!