I have woken this morning to find my right, upper eyelid twitching uncontrollably. what causes this?

Sounds like: Ocular myokymia, which is quite common and self-limited usually and very annoying, but benign. Caused most often by fatigue, eye strain, stress, lack of sleep, exhaustion, chemical imbalance, nearby infections, such as nasal or sinus, repetitive squinting, maybe blepharospam. May respond to modification of corrective lenses. See your ophthalmologist, if too troublesome.

Myokymia: Random twitching of an eyelid, which is benign, is called myokymia (an involuntary, spontaneous, quivering of a few muscle cell bundles within a muscle). Ocular myokymia, is quite common and self-limited, it can last a few minutes to a few days. It can be caused by stress, dry eyes, fatigue, caffeine, and lack of sleep. Reduce intake of alcohol/tobacco/caffeine, get rest, reduce stress, tx eyes.