Starting dating for the first time in a while, suddenly feeling intense bouts of depression?

Wondering if anybody has experienced this before and/or know why I may be experiencing this.

So I just finished a pretty grueling graduate program and for the most part I didn't have much time for a social life throughout. During the program I dated one girl which was off and on for almost two years (out of the total 6). Aside from that I messed around a bit with people here and there but nothing was serious at all.

Since I just finished the program I made a point to try to get back out there in the dating world, and I ended up reconnecting with this girl had a few classes with a few years back and turned out we had crushes on each other all along. We've gone on a few dates and to be frank I'm totally smitten. It's like every time we hang out I'm on cloud 9, and then we the few days in between dates I feel like a nervous/depressed wreck. It's a bit concerning since I felt totally content with my life just pursuing my own personal goals for the last chunk of my life and not worrying much about social things. Little to no depression or anxiety at all, and I was much more of a hermit than I am now. Now I have no urge to go for these personal pursuits that once consumed me, and I honestly just can't stop thinking about this girl.

Is there anything I can do to help this? It feels like I have an unhealthy obsession. We've spent 5 days together in 2-3 weeks but I'm already feeling this way and I know that is generally seen as moving too fast. Let me know any thoughts please :)