One thing is for sure though, we are the only ones seeing the Dreamer...
Personally, I think that the dream persona is the sentience within the artifact that Shadowheart carries.
You know what... that is actually the best theory I heard so far on who the Dreamer might be.
And it honestly really fits too because the Dreamer gets really annoyed if you keep telling it that they are the tadpole. And they also get mad for acting ungrateful; "After everything I've done for you". And especially mad if you intentionally try to choke them during the final scene in EA; "You deserve everything that is coming".
Not to mention the part where we fall from the Nautiloid, the magic looks the same as when the artefact protects us during the Absolute's mind influence. And it manifests itself to us even without Shadowheart.
So what if Shadowheart's mission all this time is to take it to Baldur's Gate so we can unlock it and free the Dreamer from within. Because Shar's followers are supposed to bring down false Gods and beliefs, so their intention is to use the Dreamer as a weapon against the Absolute. But the Dreamer sees us as its true champions instead of the Followers of Shar, so instead it becomes our own actual companion. Would make sense then why we get to customize the Dreamer at the start of the game.
Which brings this topic back to a full circle as to why long rests should not be discouraged, due to all the fascinatingly intricate story hidden behind long rests ^^
