sleeper

• one who sleeps; railroad passenger car with beds; person or thing which achieves unexpected fame or success; railroad tie (british); horizontal beam or other supporting piece
you can use sleeper to describe the way that someone sleeps, for example someone who is a sound or deep sleeper is not easily woken up.
a sleeper is a bed on a train.
a train with beds for passengers is also called a sleeper.
railway sleepers are the large, heavy beams that support the rails of a railway track.