This would depend on the reason for the swollen eye. Did you have something in your eye when you went to sleep? Did you use a new cosmetic or contact lens cleaner that you may have had an allergic reaction to? Do you wear contact lenses, and possibly forgot to take one of them out? (I actually did that once). If so, then you need to have an optometrist or ophthalmologist look at it to make sure there is no damage, such as an abrasion or scratches on the eye. Have you recently used eye drops that you coud have been allergic to, or that were expired or contaminated? Could you possibly have allergies or sinus problems that caused it? If you have sinus problems, it can cause swelling in one eye and not the other. Either way, I would advise having it checked out by your doctor. But until you can get in to see him/her, you can help reduce the swelling by cold compresses applied to the eye for about 15 minutes every couple of hours. And it would be best to not wear eye make up until you know what the problem is. Also, if your eye makeup is more than a few months old, it needs to be thrown out and replaced. Old eye makeup is one of the major causes of eye infections.