Down" is used many different ways, and its spiritual meaning in the Bible is highly dependent on context. Phrases like "bowing down," "lying down" and "falling down" are defined primarily by "bowing," "lying" and "falling"; there is also a great difference between a person descending, the Lord sending fire from heaven and someone handling an object, to offer a few examples. In a very general sense, though, "down" indicates a lowering from more internal spiritual states to more external ones. That's why the journey is described as going "down" to Egypt from Canaan, and people from all quarters go "up" to Jerusalem. It's also why the Lord comes "down" to us, which generally indicates a state of judgment.

2201. Verse 12 And Sarah laughed within herself, saying, After I have grown old, shall I have this pleasure, and my lord being old?

'Sarah laughed within herself' means the affection possessed by that rational truth that such was to take place. 'Saying, After I have grown old, shall I have this pleasure?' means that the affection possessed by that truth had no inclination to change its state. 'And my lord being old' means that the affection for truth was amazed that rational good to which truth was allied was also to cast off the human.