USB Mouse tracking suddenly, drastically slowed

Today I ran into a bug that I've never experienced before: my mouse suddenly dropped to about 1/10th of it's normal tracking speed. I use a SteelSeries wired USB mouse. I went to System Preferences and tried increasing the tracking speed, but that did nothing to alleviate the slowdown. I have use a three-monitor setup for work, so not having blazing-fast tracking isn't an option, or I'd be lifting my hand of the mousepad multiple times, just to get from one monitor to another... My Tracking Speed settings have always been 3-4 clicks away from the fastest, which still let me cross 2000-3000 pixels by only moving my mouse 3-4 inches. Now, to get across just two monitors takes 4 full 'swipe the mouse all the way across the pad, lift, set it back to the other edge, repeat (even set to the fastest tracking). Vertical tracking seems to have slowed down even more than horizontal tracking...

I glanced at several posts online regarding mouse slowdowns, so let me get these out of the way: yes, I've tried restarting. Yes, I've dried different USB ports. Yes, I've cleaned the optic on the mouse. No, the mousepad's not dirty (or new). I was just working away, and it suddenly lost all speed. Someone else suggested downloading antiquated third-party mouse add-ons, but that's not an acceptable answer: the mouse/pad/computer combo has been brilliant for the six months I've had it, and it suddenly quit working, mid-movement. The trackpad seems to still be tracking at a different speed, but I don't think it's the mouse itself?

Does anyone have any experience with this issue, or suggestions for a fix?