interview. 
Associated Features Supporting Diagnosis
Delirium is often associated with a disturbanc e in the sleep-wake cycl e. This disturbance
can include daytime sleepiness, nighttime ag itation, difficulty falling asleep, excessive
sleepiness throughout the day, or wakefulnes s throughout the night.  In some cases, com-
plete reversal of the night-day sleep-wake cy cle can occur. Sleep-wake cycle disturbances
are very common in delirium and have been proposed as a core criterion for the diagnosis.
The individual with deliri um may exhibit emotional di sturbances, such as anxiety,
fear, depression, irritability, anger, euphori a, and apathy. There may be rapid and unpre-
dictable shifts from one emot ional state to another. The di sturbed emotional state may also
be evident in calling out, screaming, cursin g, muttering, moaning, or making other
sounds. These behaviors are especially prevalent at nigh t and under conditions in which
stimulation and environmen tal cues are lacking. 
Prevalence
The prevalence of delirium is highest amon g hospitalized older individuals and varies
depending on the individuals’ characteristics, setting of care, and se nsitivity of the detec-
tion method. The prevalence of delirium in the community overall is low (1%–2%) but in-
creases with age, rising to 14% among individuals older than 85 years. The prevalence is
10%–30% in older individuals presenting to emergency departments, where the delirium
often indicates a medical illness. 
The prevalence of delirium when individuals are admitted to the hospital ranges from
14% to 24%, and estimates of the incidence of delirium arising du ring hospitalization