Try changing the monitor settings, in particular the screen refresh rate. I had a Microsoft Wireless Keyboard/Mouse set, that would have sticky keys if the monitor was at a particular refresh rate.
Anything else changed recently? New Wifi network nearby, new cordless phone, microwave oven. Most wireless keyboard/mouse devices operate in the 2.4GHz band, like most other things nowadays. There may be some new channel interference.
Some optical mice go freaky if you try to use them on shiny, glass and/or metallic looking surfaces.