Mo -
Last fall I took Topamax for about a month for my nerve pain, but stopped it because for what little (barely any at all) relief it gave me, the s/e's just wrecked me. Sometimes with any drug, you can learn to deal with adverse s/e's, IF you feel you're getting the intentional benefits of it, too. That was the not the case for me and Topamax.
The s/e's I experienced where the numbness in extremities, food tasting different, appetite severly suppressed (thus the weight loss), a significant slow in cognitive functioning, and towards the end, some pretty heavy depression along with SEVERE apathy. These are all very common side effects. The numbness and food related ones I could do with, but I think I said back then in some posts that the drug was using my brain as a playground. All you need to know is the drug is nicknamed "Dopamax"

And as I said, the last 7-8 days of taking it I was becoming extremely depressed (though had plenty in my own reality to already be sad about), but it was the apathy that really hit me by surprise. Just think of it this way - Topamax slows down the movement of neurons in your brain. Neurons are necessary for the production of seratonin, and when you have less of that being produced, it's simply biologically inevitable that you'll become somewhat depressed.
However - all of this being said, DON'T let this scare or freak you out about the drug. Hopefully you will find relief from it (have heard plenty say that it 'saved their lives') and then be willing to stick out any rough s/e's. I say stick it out because typically, those s/e's level off. As with many (if not all) anti-seizure meds (Topa, Neurontin, Tegretol, Lamictal, etc) it is very important to properly titrate up in your dosing, going at a smooth, gradual level until you reach you & your doctor's goal dose. Doing this gradual increase is what gives you your best chances of experiencing as few (and as least harrowing) s/e's as possible. From what I've read and heard, once you reach a goal dose and stay there for a little while, your chances increase dramatically of getting past most of the s/e's. It's in the titration where most of their dangers live. It should also be noted (again, from what I've learned) that apparently if you dose up or down too quickly, or even stop taking the drug abruptly, even though you are not taking the drug for its main use (helping w/seizures) but rather the off-label use of helping with nerve pain, you put yourself at great risk of actually having seizures yourself.
But don't take my word for it. Others will come, I'm sure, and do a little web searching and you'll find plenty of official fact-based sites about Topamax and other anti-seizure meds. Good luck