(HealthDay News) -- Delirium is a significant change in mental status, usually occurring during times of illness or stress, Health in Aging.org says.

Delirium -- typically characterized by difficulty concentrating, changes in behavior or temperament, and an abrupt change in a person's activity level -- may be difficult to distinguish from dementia. But Health in Aging says delirium may be treatable if caught early enough.

Delirium is somewhat common among older adults, who may also have dementia. But delirium is a medical emergency that should be reported immediately, Health in Aging says.

About 7 percent of adults 60 and older have dementia, a decline in memory and general mental function. Dementia can trigger changes in mood, increased irritability, depression and anxiety.

Though it shares some characteristics with dementia, delirium usually emerges faster.