Contact lenses, even the soft ones are not totally permeable to oxygen. the cornea being an avascular tissue gets its nourishment from the atmosphere. Hence, sleeping with contact lenses, the regular kinds used to correct refractive errors, causes hypoxia or a lack of oxygen to the cornea by acting as a physical barrier between it and the atmosphere. When this happens, the normal pump mechanism that nature provides us to keep the cornea clear and free of fluid does not function too well and the cornea swells or gets oedematous. What you would experience in such a situation would be blurred vision on opening your eyes and a dry sensation with difficulty in removal of contact lenses along with reduced sensations of the cornea. Fortunately, in most cases, where the cornea is healthy, once the lenses are removed and with the blinking action of the eyelids that act by massaging the cornea, the pump begins to work again and water is pushed out of the cornea renewing it to its former clear state. No harm done and back to normal. You are fine and no treatment is needed and you may resume wear of contact lenses keeping in mind that falling asleep with your contacts on is strongly advised against.