How does vision Hoid know he is in a vision

[Deception He/Him]

How does vision Hoid know he is in a vision? Every time that he is in one of Dalinar's SR visions, the vision version of him suddenly realizes he isn't real and gets all depressed. HOW?

[GG0z He/Him]

Pretty much, all visions are in the spiritual realm, meaning they are made of Investiture. Since Hoid has been through so much, he wasn’t only made of concentrated Investiture, which is supposed to copy people’s memories, he was also Cosmere-aware, which meant that the vision knew it was a vision. It was an overload of investiture that caused the vision Hoid to “glitch” and understand that he is a vision.

[Nitpicking]

We're all just speculating. I think the Exist dawnshard modified Hoid's soul, and also gave him so much Investiture that even his "Spiritual Shadow" in the Spiritual Realm has enough Investiture to become sapient the way Honor almost(?) has. It's not different (in my opinion) from the way the Blackthorn spren is now a sapient being, and it's like (but not the same) as the way the Stormfather created Sylphrena.

Once the Hoidspren was there and sapient, like GG0z said, it would have Hoid's knowledge of the Cosmere and realize what had happened. As Brandon wrote about in Snapshot, it isn't fun to suddenly realize you are only a simulation of a real being, and you'll shortly poof into nothingness.