What mental disorder is marked by confusion and often temporary impairment?

Delirium is characterized by a sudden onset of confusion, disorientation, and a fluctuating level of consciousness. It often occurs as a response to a medical condition, such as an infection or substance withdrawal, and is typically temporary. Individuals experiencing delirium display cognitive disturbances that can affect attention, perception, and thinking, which can vary significantly from one moment to the next. This rapid change in mental status distinguishes delirium from other disorders like dementia, which develops more gradually and is marked by a persistent decline in cognitive function over time.

In contrast, dementia refers to a group of disorders, including Alzheimer's disease, where cognitive decline is progressive and chronic. Alzheimer's disease is a specific form of dementia that leads to further impairments in memory and daily functioning. Mood disorders, while impactful on cognition and emotional states, don't typically present with the acute confusion that defines delirium. Therefore, the hallmark of delirium is its confusion and the often transient nature of impairment, making it the correct answer in this context.