mouse scroll suddenly jumps like an entire page

Ok this might be the DUMBEST question ever. I remember I had this problem before but I have ZERO recollection on how to solve it.

Suddenly my mouse wheel, when scrolled, jumps about a page up or down at a time, rather than gradually spinning through the tracks in the editor. I’ve checked my windows settings, they haven’t changed, and I’ve set my scroll to be the lowest (1 line at a time). No help. Has anyone seen this before?