The relationship between delirium and dementia is being explored by scientists investigating a possible link between the two.
Delirium is an acute decline in a person's ability to focus leading to feelings of confusion.
Over four million older people in US hospitals develop symptoms – which can include disorientation, paranoia and hallucinations – every year.
Dementia, including Alzheimer's disease, is a potentially devastating form of cognitive decline affecting nearly 24 million people around the world.
The conditions are widely thought of as distinct but the latest study asks if delirium and dementia could represent different ends of the same spectrum of disease.
"I have been studying delirium for 20 years," said Sharon Inouye, a director of the Aging Brain Center at the Institute for Aging Research.
"And the more cases I encounter, the more linkages I see with dementia.
"For a large proportion of older patients, the problem [of delirium] is never resolved. I routinely hear from patients' families: 'They went into the hospital, they became very confused, and they never recovered'."
Aging expert Luigi Ferrucci added: "Better understanding of delirium may represent a new window of opportunity for the prevention of dementia.
"We, therefore, decided to approach the subject from a multidisciplinary perspective, exploring delirium and dementia from a number of vantage points."
The study appears in this month's Journal of Gerontology.