Did you watch the movie Inception?
The plot was.... a team of highly skilled agents would enter the subconsciousness mind of a subject with the view of extracting and stealing valuable secrets while interacting in the 'dream' which was manipulated.
My point is.....each 'agent' would carry something personal that only they knew, that kept them grounded, so they would recognise what was 'real' or what was the manufactured 'dream'. Much like your pet rock in your pocket, Peter.