There are many causes for eye pain. Eye pain is described in two big categories, ocular pain and orbital pain. Ocular pain refers to the outer tissues around eyes, including pink eye, stye, belpharitis, corneal brasion or ulcer, chemical burns. While orbital pain is described as deep and dull pain in eyes, which usually refers to glaucoma, iritis, optic neuritis, migraines or trauma. I don't know what kind of pain you are suffering from. If you are alright before taking a nap, and then you get this pain, I am not sure whether you were wearing contact lenses while you were taking nap. Wear contact lenses during sleeping is very bad for eyes. It can easily cause corneal abrasion. According to the contacts lenses wearing guide and introduction from doctors, it is prohibited to wear contact lenses while sleeping. This is my guess. I suggest you to take the lenses off now to give your eyes a break. If you can, apply some wet compress to relieve your pain. However, if you didn't wear any lenses, and your pain is severe, I suggest you to visit your ophthalmologist to find out what is the direct root, so that he/she could provide proper treatment.
