iMac mouse left click sometimes unresponsive?

Before you say it's the mouse, it isn't.

Randomly, when the iMac has been asleep for a while, or sometimes even when you're in the middle of doing something, the left click stops working. Right clicking works fine, but left clicking does nothing. My mouse worked fine until I got OS X 10.9.2- could it be some kind of glitch? The battery level on the mouse is fine, around 62%. What's going on?

Thanks for the help.

 

As I've said, it happens randomly, which makes me think it isn't the mouse. Another thing I forgot to mention- I can move the cursor everywhere still, and when I hover over the dock (I have magnification on) it magnifies normally, then freezes and stays like that. The right click still works, and I can restart the system still. This is why I am thinking it's more of a glitch in the system.