Chronic ciguatera can be confused with CFS. Ciguatera is a distressing form of fish poisoning caused by the ingestion of one or more of a series of ciguatoxins. These poisons, some of the most potent mammalian neurotoxins known, are manufactured in reef-dwelling dinoflagellates and concentrated up the piscine food chain. Humans become poisoned be eating certain bottom-dwelling fish species. The acute intoxication is clinically dramatic, resulting in parasthesias, dysesthesias, prostration, myalgia,and arthralgia. in approximately 20% of cases, symptoms of fatigue, reduced exercise tolerance, and nonspecific headaches and pains persist for months and, in a small percentage of cases, for years. Occasionally, patients are encountered who have been diagnosed with CFS because of a lack of awareness of the ciguatera syndrome, but in whom in retrospect the episode of acute fish poisoning can be established.
(Source: Concise Encyclopedia of Chronic Fatigue Syndrome, by Roberto Patarca-Montero, M.D., Ph.D.)