I always wondered (looking at it rationally) if people see Sumerian things, entities, or whatever because they read about others seeing that. One person could have had this experience and it mushroomed. Even if you don't intend to, it may lurk in your subconscious and manifest in the trip.

You didn't inadvertently suffocate yourself did you? I like to read about/listen to people's accounts of NDEs and that sort of thing usually seems to happen when people drown or go into cardiac arrest. Is this is a common thing? I've never actually inhaled plain old DMT before.