The best way to find a lens in a situation such as the one you are describing, is to let a professional have a look at it. If it is stuck under the eyelids (it is not possible for it to disapear behind your eyes) somewhere, it is best found by your optometrist using a fluorescent dye (no pain involved) that can be put into your eye. This will make the lens glow very bright when a special blue light is shone on the eye. This will make it easier to tell whether the lens is indeed still in your eye or not. If you ever suspect that your lens is still in your eye, call your optometrist for advice.