An amazing article about research of psilocybin: http://www.newyorker.com/magazine/2015/02/09/trip-treatment
There's a passage about "default-mode network" in brain which orchestrates other parts, filter their communications and acts as the "ego". In the mystical state it's suppressed - the filter level is decreased. So the hypothesis is actually consistent with results of some research using fMRI. Nice. :)