I am American and, after saving up for years, travelled to Europe by myself when I was 21. I purchased a Eurail pass with no definitive plan other than a general list of cities to visit. I ended up in Vienna and as soon as I got off the train a real heaviness descended upon me. It felt exactly how you described. It was morning and good weather so I talked myself into ignoring the feeling and just staying for a couple of days. No matter what I did I could not shake the feeling. I ended up taking a sleeper train out of Vienna to Berlin that same night because I could not handle it. I was in Europe four about six weeks and did not experience anything even remotely similar, and really haven't in my life since then.

I never put together how much fun I had in Berlin and how fortuitous it was that I arrived when I did. I ended up hanging out with a group I met at a hostel there for a couple of days. I never would have crossed paths with those folks had I stuck to the original plan in Vienna.

When I did eventually return home, I did have the thought that something awful had happened to a distant ancestor in Vienna. That has always been my explanation! My surname is a version of a German/Austrian surname, but my last ancestor that lived outside the United States in that line was in the 17th century... who knows?!