The visions produced by mescal and other hallucinogens would usually
progress from these elementary forms of hallucination to elaborate
visions of a much more personal and sometimes mystical sort (including
scenes of people, animals, and landscapes). But Klüver remarked that the
lower-level, geometric hallucinations that preceded these were
identical to those found in a variety of conditions: migraine, sensory
deprivation, low blood sugar, fever, delirium, or the hypnopompic and
hypnagogic states that come immediately before and after sleep.