I woke up with a light purple spot under my upper right eyelid, what could cause this?

Probably bruise: Without a photo, I'll be guessing. I suspect a bruise of the upper eyelid may have occurred. Often painless and self limited, usually the result of running the eyelid. Other considerations would be a insect bite, vascular lesion, sty, nevus, dermatological condition to name a few. As I mentioned, lesions, benign or malignant, are best examined by a clinician to provide you with a definitive answer