The Ambulance (1990)

Josh Baker meets a very special woman, Cheryl, on the streets of New York City. Suddenly she collapses, and she's picked up by an ambulance. When Josh wants to visit her in the hospital, it appears that she hasn't been admitted to the hospital. Josh follows Cheryl's roommate, and she disappears after a ride in the same ambulance. It's up to Josh to solve the secret behind this strange vehicle.