Carry On Dancing (1988)

Cheung Sheung and Tze Ngor are twin sisters. Tze Ngor is a lunatic and stays in a mental hospital. But out of a madcap incident, Cheung Sheung is "cheated" into the hospital, exchanging identity with her insane sister. The mad house is lived by all kinds of weirdos. The "game" is that Cheung Sheung will stay in the hospital only for a while. But strangely enough, she gradually becomes more and more ease with the way of life in the hospital until one day, she's forgotten what life is like...