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.

8279. 'They sank down into deep places like a stone' means that they fell down to lower levels as if on account of heaviness. This is clear from the meaning of 'going down' - down to lower levels as if on account of heaviness - as falling down; from the meaning of 'deep places' as lower levels where the hells are located, dealt with below; and from the meaning of 'like a stone' as, as if on account of heaviness. The words 'like a stone' are used because 'a stone' in the genuine sense means truth, dealt with in 643, 1298, 3720, 3769, 3771, 3773, 3789, 3798, 6426, and therefore in the contrary sense means falsity. Furthermore falsity arising from evil is by nature such that it falls downwards to lower levels like a heavy object in the world, whereas truth springing from good is by nature such that it rises upwards to higher levels like a light object in the world. This explains why the evil who have not yet undergone vastation in respect of the truths they know are in the region above hell; but as soon as they have undergone such vastation, that is, have been deprived of truths, it is as though they have had their wings cut off and they fall downwards like weights. And the worse the falsities arising from evil are, the further down they go.

[2] So it is that 'deep places' means the hells, just as 'depths' does; but 'deep places' means the hells in respect of evils, while 'depths' means the hells in respect of falsities arising from those evils, as in Jeremiah,

Flee! they have turned themselves away, they have taken themselves down to dwell in a deep place. Jeremiah 49:8, 30.

In David,

The waters have come even to [my] soul, I have sunk in the clay of a deep place, and there is no standing; I have come into the deep places of the waters, and a wave overwhelmed me. Snatch me out of the clay lest I sink; let me be snatched from those who hate me, and out of the deep places of the waters. Do not let the flow of waters rush over me, nor the deep place swallow me up, nor the pit close its mouth over me. Psalms 69:1-2, 14-15.

In Micah,

He will cast all their sins into a deep place in the sea. Micah 7:19.

The reason why 'a deep place' means hell in respect of evil is that it is the opposite of 'a high place', which means heaven and is used in reference to good, 8153. Evil also corresponds to a heavy object on earth that falls downwards on account of its weight, and so corresponds as well to the heaviness of a stone, when 'a stone' means falsity.