Delirium (also known as acute confusion)  is medically recognized as a physiological disturbance of awareness that is accompanied by a change in baseline cognition which cannot be better explained by a preexisting or evolving neurocognitive disorder. The disturbance in awareness is manifested by a reduced ability to direct, focus, sustain, and shift attention and the accompanying cognitive change in at least one other area may include memory and learning (particularly recent memory), disorientation (particularly to time and place), alteration in language, or perceptual distortions or a perceptual-motor disturbance. The perceptual disturbances accompanying delirium include misinterpretations, illusions, or hallucinations; these disturbances are typically visual but may occur in other modalities as well, and range from simple and uniform to highly complex. An individual with delirium may also exhibit emotional disturbances, such as anxiety, fear, depression, irritability, anger, euphoria, and apathy with rapid and unpredictable shifts from one emotional state to another. 
This disturbance develops over a short period of time, usually hours to a few days, and tends to fluctuate during the course of the day, often with worsening in the evening and night when external orienting stimuli decrease. It has been proposed that a core criterion for delirium is a disturbance in the sleep-wake cycle. Normal attention/arousal, delirium, and coma lie on a continuum, with coma defined as the lack of any response to verbal stimuli. 
Delirium may present itself in three distinct forms. These are referred to in the scientific literature as hyperactive, hypoactive, or mixed forms.  In its hyperactive form, it is manifested as severe confusion and disorientation, with a sudden onset and a fluctuating intensity.  In its hypoactive (i.e. underactive) form, it is manifested by an equally sudden withdrawal from interaction with the outside world accompanied by symptoms such as drowsiness and general inactivity.  Delirium may also occur in a mixed type in which one can fluctuate between both hyper and hypoactive periods.
Delirium is most commonly induced under the influence of heavy dosages of deliriant compounds, such as DPH  , datura  , and benzydamine. However, it can also occur as a result of an extremely wide range of health problems such as urinary tract infections  , influenza  , and alzheimer’s  .
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