Turn in for the night

What is the derivation of "turn in for the night"? i.e go to bed.

One of the meanings of "turn" is "move in a particular direction". When you turn in for the night, you go, or "turn", *in* to your bed. In the morning, you get, or "turn", *out* of it. (You can also "turn out" the guard in a military emergency - this is a similar usage.) (VSD_