Hi ImScared,
I can't really offer any kind of diagnosis or prediction; that's what you're having the exam for.
What I will tell you is, the exam is JUST an exam. You'll get x-rays, and the dentist will probably ask to have a look inside your mouth. He (/she) won't touch anything sensitive or cause any pain-- he'll typically use a mirror and something that looks like a pick, but that's really just to move your tongue out of the way. Dentists know better than anyone not to just go poking at teeth that might hurt.
Between the x-rays and the visual inspection, the dentist should have a pretty good idea what treatment you need. He'll probably call out each tooth and what it needs to the assistant, who will note it in your records. And then, you can sit up and talk about what needs to be done and what, if anything, is a priority.
Almost nothing in dentistry is an emergency-- my mouth was full of broken, jagged, shattered teeth when I went in, and I thought they'd immediately freak out and want to start pulling them right there. But the dentist was very calm and just told me that we'd talk after the x-rays.
Once you know the prognosis, you can decide when, how much, and if you want to have any of the work done. If something is actively causing you pain right now, you'll probably want to take care of that sooner, for your own comfort. But the dentist doesn't care. You should also expect not to be shamed or scolded-- you're an adult now, and perfectly entitled to however you want to keep your teeth. The dentist has seen much, much worse, and won't be alarmed or upset with you. He just wants to help you fix your teeth up.
That's really all you should expect tomorrow-- xrays, a visual exam, and a conversation. If the dentist wants to do a cleaning or some additional work, he should ask your permission before starting, and you're COMPLETELY entitled to say, "No, I just want the exam today." That's really very common. No one will force you to do anything without your consent.
Hopefully that helps set your mind at ease, a little. One last word, from someone who's been there myself and has advised hundreds of people on this forum: it's almost always way better news than you anticipate.
Good luck, and good for you for making the appointment and getting yourself there. You'll do great.