Is it normal to constantly think about something?

For the last few months or so I've been upset by listening to the conversations of strangers and obsessed by not knowing things. I'm in law school and I've had a tough time making new friends. I still talk to many of my friends from College but not as regularly and I don't see them as much because we've all gone our separate ways.

Anyways, when I hear a song or a snippet of a conversation I sometimes feel as though I HAVE to know what it is or how it ends. For example, when I hear a song sometimes I think 'I HAVE to know what song this is' and Shazam it immediately. If I can't shazam it sometimes I get anxious.

Here are a few other prominent examples:

Roughly 2 months ago I had a panic attack in my library while doing work because I didn't think I'd ever be able to remember the name of a movie I saw when I was young. I put it on reddit and a few days later I was able to figure out the title (Teen Knight). The thing is I'm actually afraid of how upset I was that I couldn't figure out the name of a movie--it was like I was going to die if I couldn't get it.

I also began having occasional anxiety and panic when I was on the bus because I would think, 'oh no, I can't get off!' even though in my mind I knew that I didn't want to get off.

I had anxiety one day when my mom and I got our Christmas Tree at Goodwill and I left a book (the Pelican Brief) in the wrong place on a bookshelf. It really bothered me all the way home, and I ended up having to go out and buy the book so that I would feel better.

I had anxiety while on the train one day because I saw a part of what a woman was watching on her iPad and got curious--what was it? I then realized that it was Hawaii 5-0 when I got home, but the idea that I might never know really bothered me, and I considered following her off the train.

The very WORST time, I was in the subway buying a monthly pass and I heard a man having a conversation about his ex wife or something, and it sounded so interesting. Midway through, I was asked to go outside the office because I was one of many people standing because there were no chairs and the rule is that you must sit while in the office. I got really anxious that I never heard the end of the conversation and didn't get any closure. I went in when I got called and got my ticket but then I had an anxiety attack. When I was done I waited outside for about 20 minutes for him to get called and took a picture of him because I was so worried that I'd never know how his conversation ended. I then followed him to Downtown Crossing where he got some food but I forced myself to leave after a few minutes because I didn't think I could do anything and I knew that what I was doing was wrong. Afterwards I walked around a city park in a miserable mood and almost walked over to a counseling center for an emergency appointment. My phone died and my computer had no charge. I actually cut class to do all of this. Then, I went to buy some candy at Walgreens and went to the bus stop. I caught a bus but had to walk home from the middle of town because my phone was dead so I couldn't call for a ride.

I was miserable for a few days before I had to buck up and get to studying for my finals.

Months later I still think about this day and I wonder if I'll ever get closure. I spend most of my time thinking about whether I'm 'fixed' and whether I'll ever be able to quiet my mind again.

This is all basically background info I guess. My question is: Is it normal, or am I just overthinking all of this.