My girlfriend and I have both had similar experiences, quite "dark" and scary.
For me it even changed midway from nice to that sensation of stillness, eerieness, stupidity, not understanding anything, confusion, utter fear, etc.
Both times, it was when using repeatedly in a short time and under the effects of LSD.
Perhaps, LSD is not needed, and the repetition is enough to achieve that awful state, so we've been taking care of leaving at least an hour of rest between sessions.
The sensation was terrifying, my girlfriend had a proper panic attack. I handled it well, perhaps because it happened first to her, but definitely not nice and would not want to experience it again ever.
Let's be honest: the Questionnaire is toooooo long and deep!
"One has a moral responsibility to disobey unjust laws" - Martin Luther King