The simplest way is to look into the distance. If you feel the things are blurred and your eyes are still comfortable, your contact is fallen out. If you feel the things are blurred and your eyes are not comfortable, your contact may move into your eyes. The second way is to touch your eyeballs with your hand gently. Remember, you must wash your hand clean. If your eyes don't have any feel, your contact must still in your eyes because it is the contact that touches your eye. If your eyes blink as a kind of conditioned response, your contact must have fallen down because your eyes will response to the outside touch automatically. If sleep without taking off the contact lenses and they moved into the eyes, you may need to see a doctor to take them out.