It's unfortunate that contact lenses are too small to have beepers for these moments of panic.
If you have dropped a lens into the sink, plug the drain immediately and turn off the water. Gently pat the sink and surrounding area with your fingertips to find the lens. (If it went down the drain, see How to Rescue an Item From the Sink.)
Check your clothing carefully to see if the lens fell into a sleeve or got caught in a hem or pocket.
Ask everyone who is searching for the lens to remove their shoes. Someone might discover it by stepping on it.
Turn off the lights and search the vicinity with a flashlight or bright lamp. Get down so you're at eye level with the floor and look for any glint from the lens.
Place a nylon over the end of a vacuum hose and secure it with a rubber band. Keep the nozzle about 1 inch (2.5 cm) above the floor. Turn on the vacuum. The nylon will catch the lens.
Clean, rinse and disinfect the lens before you place it in your eye.