You haven't clicked on the centre wheel by any chance?
This (depending on your mouse features) brings up a small circle with arrows pointing up and down - it allows rapid up, down and (if appropriate) side to side scrolling by moving the mouse.
The Evil Within 2 review-in-progress
Photoshop CC 2018 released with new Curvature Pen and better brush tools
Camera tips to take better iPhone photos
Les meilleures applications de covoiturage 2017