Ergot poisoning

Ergot poisoning is a rare form of toxic reaction to exposure to the ergot fungus, which is the source of lysergic acid diethylamide or LSD. It is currently very rare, but was more common in centuries past (where it was often mistaken for demonic possession) as the ergot fungus grows well on grain, particularly rye, which is kept in moist conditions. The fungus is not destroyed by milling or cooking (although it is destroyed by refining), so cooked whole grain products can also be contaminated. 
Persons who ingest ergot suffer similar hallucinogenic effects of LSD, plus because the dose is typically higher than what is used for recreational purposes, it also results in heightened physical symptoms which often vary greatly depending on the patient. Such symptoms can result in the death of the patient if the dose is large and the symptoms are severe.
Antidepressants can suppress the effect of the LSD, but the symptoms will disappear in time if the patient is not exposed further.