Needless to say, everyone's mouse slows up eventually.
Most of the time it is due to some lint on the ball and on the rollers.
To remedy this, when the computer is shut down, do the following:
1.Open the mouse from the bottom by turning the round door-opening
(older mice need to have some screws removed).
2.Remove the ball and using a swab and some denatured alcohol,
clean the ball.
3.Look inside the mouse and locate the round bars.
Lint from the mouse pad gets picked up by the ball and
then deposited on these bars.
Since the movement of the mouse is transferred from the ball
to these rollers and then on to the computer, any
interference can cause the problems you are describing.
With the swab, gently remove the lint from the
rollers and your mouse should work much better.