Delirium Definition: A sudden onset of acute confusion and hyperactivity. The 1999 edition of the Merck Manual defines delirium as follows:"A clinical state characterized by fluctuating disturbances in cognition, mood, attention, arousal and self-awareness which arises acutely...."Distinguished although similar to dementia. Generally, delirium develops rapidly while dementia usually develops gradually. Delirium may be reversed; dementia, once established, rarely is. Further, delirium can require emergency medical attention whereas those that suffer from dementia do not generally require emergency treatment.REFERENCES:Beers, Mark and Berkow, Robert, editors, The Merck Manual of Diagnosis and Therapy, 17th Ed. (Whitehouse Station, New Jersey: Merck Research Laboratories, 1999), page 1393.Duhaime, Lloyd, Duhaime's Legal DictionaryDuhaime, Lloyd, Duhaime's Legal Citations & AbbreviationsPugh, Maureen, (ed.), Stedman's Medical Dictionary, 27th Ed. (Baltimore: Lippincott Williams & Wilkins, 2000), page 470Schmidt, J.E., Attorney's Dictionary of Medicine, Volume 2 (Newark, New Jersey: LexisNexis, 2009), page D-50 Categories & Topics: Medical-Legal Dictionary Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!