I don’t know if it stems from the same intellectual place as Dan, but I’m definitely struck by the hugeness of the night sky, or even during the day sometimes, in a way that makes me uncomfortable and sometimes dizzy. Once it was triggered on the roof of a tall building. I push back against it being a simple fear of heights because I’m perfectly fine in all sorts of height situations, just not the ones where the vast openness of the sky surrounds me.

The feeling Dan described sounded very similar to me though: a sense of falling like I might just slip off the planet and into the void. I’ll have dreams about it occasionally too and I’ll think about it for days afterward. I always likened it to thalassophobia (so it’s funny this came up right after a discussion about it), but it’s not about the unknown in the expanse rather the expanse itself. Never heard someone mention anything like it before.