When I travel solo, I become much more introverted. I think that being in your own head has a stickiness to it, so if you're in it for a while, it's hard to snap out of it. You can also be quite weary after a day on the road.

You might also find solo travel difficult when you're around other people. I love solo travel when I'm in nature, but Friday nights in cities can be dreadful.

Still, you will meet people. You don't have to be extroverted, just open to talk. If you're not curious, other people will be. They'll throw you the ball. You just have to throw it back. Bless these people.

However, the stereotypically cold Germans were actually highly receptive of a random stranger talking with them. I was invited to changed destinations a few times to hang out in random cities, and started a couple friendships.

Of course those were also people taking advantage of the 9 euro ticket, so there's a lot of selection bias here. :)

I also think that if you're avoidance strategy is withdrawing from social life, changing your location and not staying in all day is the key ingredient. You can't get your needs met at home.

This is what helped me, when I was in that position.