Based on my experience, and measurements I've made over the years, I would say that one or both of two things happened:
1) You triggered the voting ring detection code, and/or
2) You got several downvotes.
I do feel that there is a sizeable collection of people here on HN who, for whatever reason, don't like discussions about philosophy of consciousness and similar. If you get 10 or so downvotes and only 10 or so upvotes, your item will sink to the 1000s. I have seen it happen. (based on surmise about flags - they are not explicitly visible.)
This discussion happened recently: https://news.ycombinator.com/item?id=3890565
The item was flagged dead, but the discussion is still there.
HN remains a remarkably civil forum, and perhaps the occasional apparently draconian measures are part of the price to pay.