Nothing really terrible comes to mind.
I've had the usual share of pre-booked hotels that turned out to be uninhabitable flea-traps. (Say... am I the only one who isn't paying by the hour?) Or the reservations were lost entirely, or not honored.
A few in-flight emergencies. Lost luggage. Cancelled flights.
One time in grad school, I scraped together enough money, barely, to go home for vacation on one of those "People's Express" flights. The plane landed at midnight, somewhere out in fly-over country and the pilot announced. "This airline is going out of business and is ceasing operations. Now."
I spent the night sitting outside the airport gate. Phoned home the next day to beg someone to buy me a new ticket to get the rest of the way home. I never did see my backpack again.
One sort of surreal episode happened on my second-ever trip away from home (not counting scout camp and the like.) I was seventeen and flying by myself to Costa Rica to meet a group for one of those four-week exchange programs. However, that was also the day that President Carter chose to send the US Marines into Nicaragua to rescue the dictator Somoza from the revolution and fly him to Miami. Apparently they were broadcasting ahead on the radio, telling all aircraft to land or be fired on. The plane that I was on made an unscheduled landing in San Salvador. I had to stay there for a couple of days, while the airline waited to see if a war was breaking out, and then figure out when it was safe to re-schedule the flight.
El Salvador was not very friendly toward the US at that time, and had revolutionary problems of their own brewing. I remember a long strange ride in a van through narrow streets strung with anti-US banners. I had no idea where we were going. I had no visa to be in that country. I could barely speak a dozen phrases in the language. Eventually, we ended up at a beautiful modern hotel, on a hilltop above the city. The place was nearly empty. The walls in the lobby and patio had photographic murals of "Miss Universe" contestants. (I guess the pageant had been recently held there.)
In the gift shop, I found two english-language paperback science fiction books.
I sat on the patio for a couple of days, reading those books, drinking cokes, and looking down at the slums below the hotel. (One of the books, In the Ocean of Night
by Greg Benford, in an incidental plot twist, has my home county being obliterated by a nuclear explosion, accidentally set off by Sasquatch... er... it makes sense in the book, sort of. Anyhow, it just added to the surrealism.) Nothing more actually happened. Eventually we went back to the airport and resumed our trip.
But later, I frequently saw that hotel on TV news, during the revolution. Apparently it was the site of frequent gun battles (or perhaps journalists were housed there?) Sometimes, a machine-gun nest could be seen on the patio, where I spent those two days, just a few months earlier. The wall with the Miss Universe mural was pocked from gunfire.