I'm not aphantasic, but experience something very similiar I guess. Sometimes when I'm exhausted and close to falling asleep, I experience very clear images of either faces or rooms. The faces always belong to people I know personally, change shape, then as soon as I become aware, they fade almost instantly. As for the rooms, I get the impression of being able to see with closed eyes. Usually I'd see my blanket, random items (such as a chocolate bar laying around) and room interior. Again these are very clear, but fade rather quickly.

This phenomenon I found referred to as astral projection[0], mostly in esoteric circles.

[0] https://www.reddit.com/r/AstralProjection/comments/7ofaol/se...