It's possibly a mineral deficiency. Sodium, Magnesium, Potassium or Calcium--make sure you're getting enough of each of them. Each of the last two years, I've ended up with an eye twitch for about a month or more, and it turned out the first year was a potassium deficiency (I started eating 2 bananas per day, and it was gone within 3 days), and the second year, I'm not entirely sure, but I think it was magnesium and sodium (the bananas didn't work, so I ate more potato chips and took magnesium supplements, and it faded away over the course of a couple weeks).
Again, just a possibility, I'm no doctor, but I'm in really good health.
Jason