Comment by D-Machine

I can almost always tell the projection and reality are different, but in some very rare and extreme cases (psychedelics, sleep deprivation, extremely protracted and deliberate meditative focus / practice, or e.g. in situations where the projection is properly aligned with the actual stimuli, like seeing a face in the clouds, or in vivid / lucid dreams), the differences can be so small that what allows you to distinguish the two can simply be knowledge of the will / effort involved or e.g. knowledge from laws of physics that what is visualized cannot be present, or, in the case of dreams, an inconsistency with autobiographical memory.

Otherwise, yes, in almost all other cases, I suspect our experiences aren't that much different.