I woke up this morning and found redness on my top eyelid , how bad can this be?

Sty: Is mild eyelid infection. Use warm compresses for relief.

Usually not bad: Swelling in the eyelid is usually caused by a hordeolum, also called a stye. There are glands in the eyelids that produce oils that help lubricate your eye and contribute to your tears. Sometimes, these oils get thick and can clog the gland. This leads to redness and swelling. Usually these resolve on their own but some heat applied to the lid can help it along.

Probably not serious: It could be that you slept on that side and irritated the eyelid. It may be that you are developing a sty in the hair follicle coming out of that lid. Would place some cool compresses on the lid, wash the face several times a day, and see if it goes away. If the whole eye becomes red, or itchy, or painful, see your pcp, who will be able to treat it, or if necessary will refer you to an eye doc.