If you are of Chinese descent or have friends who are Chinese, you would probably have heard of tonnes of superstition concerning the twitching of eyelids. Some say if your left eyelid twitches, it'll bring you good fortune, while if your right eyelid twitches, it spells impending misfortune.

But we'll not dwell upon these wive's tales any longer, and instead give you a scientific explanation of the twitching.

These "twitches", are called Fasciculations. Refer to the video I've embedded below to have a clear picture of what I'm talking about here.

Fasciculations simply means the involuntary contraction and relaxation of our muscles beneath our skin. It usually occurs in rapid succession, for a period of time ranging from a few seconds to a few minutes.  These contractions will go away when you try moving the muscles voluntarily, but annoyingly, they tend to come back immediately after you rest the muscle.

The reason why fasciculations happen is not fully understood, but we DO know a few common causes of fasciculations. The most prominent one will be Magnesium deficiency. If you had a very bad episode of diarrhoea, or vomited, there is a high chance for you to lose your serum electrolytes, one of them being magnesium. Of course, an imbalanced diet or malnutrition can also lead to Magnesium deficiency in the long run.

Another common cause is the intake of certain Over-the-counter medicine like Cough syrups containing diphenhydramine (Benadryl, Bena Expectorant, Dynadryl etc). The very popular motion sickness prevention pills Dramamine and Novomin too may trigger fasciculations. 

Food and drinks containing caffeine will too increase the chances of you getting fasciculations. And any combination of the above risk factors will increase your chances greatly.

So picture this:

You are about to get on a plane to journey far away, and you take Novomin for motion sickness. The next morning, you awake having jetlag, and drink double your normal intake of coffee to stay awake. While travelling, you eat something from the streets, and end up rushing to the toilet purging. After you come out of the toilet, your left eyelids start twitching like mad, and you go buy some lottery tickets because you think good fortune is coming.

After all that has been said, more than 90% of fasciculations are benign and do not pose any danger to our health. And almost ALL of us have experienced it at least once in our lives!