Melanie, When was your last eye exam? It could be Mestinon but it could be a boat load of other things too. Eye strain, electrolytes being off balance, circulatory problems or even tensing up muscles while you are sleeping! It couldn't hurt to see your primary doctor to at least take a fresh look at the twitching to see if it's something worrisome or something you have to live with.
When I get twitching, because I have fluid "shifting" issues due to capillary permeability, it's due to electrolyte issues. What's funny is that the twitching I had while growing up went away after taking Mestinon.
I hope you can figure it out and that it stops. That would be pretty annoying to have going on for a while.