What is it like to be a professional game tester?

Hi, you have some great insights into your own question and you asked one of the things that even most adults don't think about, which is "what will be my physical (and mental) day to day experiences".
To answer one aspect of your question, testing is a LOT of sitting. Any job in the game industry or deeply involved with computers will be. There's more awareness by people in the industry to stand up or move a bit, and slightly more awareness by companies to support those behaviors , but it's gonna happen...

Game test leads and managers, often called QA (Quality Assurance) positions, are some of the more stable job positions I've experienced. I'm talking 4+ years exp. and beginning to be a manager, not still a tester in a seat with a controller. Regular game tester positions are more often than not, not long lived (9-12 months), with temp positions with publishers like Microsoft. Unless you somehow land a job with a great company or FTE (Full Time Employment) at a publisher, my Seattle-based experience and experiences of people I've known mostly fall there.

It may not matter at this point in your life, but at some point it may be important that many other roles in a game company/publisher experience layoffs while the mid-high ranking QA people do not (or last to let go).

Game testing IS fun. I've tested Halo 3, Forza 3, Gears 2, and about 100+ game titles spread over 3.5 years as a tester (and in a bit I'll explain how someone touches 100+ titles in just 40 months). And there is some goofing around, sometimes a challenge to do a 'rabbit run' (how fast can the game be completed), but the greater percentage of time is required tasks that need to get run through.

So your definition of fun, your definition of job satisfaction, may determine if you want to pursue a long term career in QA. If you do not like the idea of going through a small hill of test passes that cover subjects like every UI menu, every decal in a car game loads, every memory and save item saves/loads/deletes, etc.. Then you MAY not like what over 50-70% of game testing is.

But every job in the game industry has required work that is less than amazing. Artists have to figure out why textures get weird only when imported into a game. Game designers have hours of coding, bug fixing, technical writing and solving publisher demands with 50% of the manpower and 25% of the time needed. And programmers?... Those poor souls have to deal with us poorly describing game behavior, changing ideas, and the same outrageous expectations that designers get.

But game testing is the most fun and free time I have seen or experienced besides seeing how much my game artist friends have to work. I got to find a bug in Halo 3 that let people auto kill with a two-shot combo. I found 50+ holes in the universe on Forza 3 and how to crash the game with audio. And because I live in Seattle, I got to work for Microsoft, who sometimes puts you on a game for 6+ months, and sometimes you work on more experienced teams that do high-octane work on a title for 1-2 weeks.

And that exposed me to scores of game engines, 70+ Dev tools to break/record/debug games, and literally thousands of test passes that taught me how games are structured, where they break, how good and poor communicators write up test passes, and where are hidden demons and show-stopping bugs that no one ever saw coming.

It taught me all of that. It made me into a stronger game desinger with an intuition about game mechanics that (my ego says) may be stronger than some other people. And having a testing background made my art and programmer friends stronger as well. It will teach you lessons not only about games, but how to act socially in an entertainment industry.

Because that is what the game industry is; the entertainment industry. And the old saying is that the entertainment industry is a people industry. So it's just as important about not being a big jerk as it is in Hollywood or TV.

But most importantly, it taught me humility. Culturally, game testers are the bottom of the heap (not QA Managers, they are quite respected), but that humility taught me to listen for alarm bells when my game design lead said something important, or if I was reprimanded how game breaking or large of a scope had I messed up. It taught me to treat game testers and artists with more respect and care. It made me stronger in empathy when I don't HAVE to, and the benefits from that change have never stopped since.

You already seem like you have a forward thinking mind, and if you are good at remembering details, anticipating problems, creating and following schedules and seeing patterns (in both real life and in games), then QA (game testing) and maybe QA Management is a great fit for you.