Worries: I did my undergrad in a department with a really unhealthy social culture. I was pretty unhappy and felt like those years were a waste. The grad students I met were more often than not pretty miserable too. I think part of the reason for this was because the school was in a more secluded location, without much of a social scene. Most of the grad students who stay on campus after their first year either have families, or are social misfits. I guess I'm concerned more broadly about making sure that I either go into grad school with or meet in grad school a group of strong friends and peers who aren't academics and won't feed into an unhealthy feedback cycle of constant work, stress, depression, and anxiety related to my work.
I'm also worried whether academia is the right move for me right now. I've been very fortunate to spend a few years after my undergrad degree working outside of academia. I think that my work is really rewarding, and I'm also well-positioned to plot a fulfilling career trajectory in the industry. The graduate programs I applied to have close to nothing to do with my professional work, so I feel like the choice I make will dictate what the rest of my young life will look like.
Excitement: I spent a lot of time in undergrad studying things that don't really "matter." The work I do now has real risks and consequences for real people. Of course not all academic work is or ought to be irrelevant to people's lives, but as bad as this attitude might sound, I also would like to be back in a place where the world won't end if I take a sick day, or don't finish a reading.