I was playing around with some settings (none of which involved tool options) and now it seems like the freehand brush tool constantly lags, like it has a "weight" to it. I never used the stabilization tool before, but I suspected it could be the cause, so I turned everything off (no smoothing, 0 distance, 0 stroke pressure, no smooth ending, no assistant) but it stays "weighted." What else could it be?

Turned off OpenGL and it fixed the problem.