Sudden confusion and altered mental state: causes, red flags and what to do

The NHS describes a confused person as someone who may not think or speak clearly or quickly, may not know where they are, struggles to pay attention or remember, or sees and hears things that are not there. When this develops over a short time and fluctuates, it is called delirium, sometimes labelled an acute confusional state.

NICE CKS defines delirium as a disturbance of cognition, attention, consciousness or perception developing over hours to days with a fluctuating course, that is not better explained by a pre-existing or evolving dementia. It usually results from an underlying predisposition meeting an acute trigger. Risk factors include being over 65, dementia, frailty, several health conditions, sensory impairment and malnutrition.

The NHS cautions against self-diagnosing the cause. The list below combines the NHS and CKS lists with a note on what often points towards each.

The NHS is unambiguous: go to A&E or call 999 if someone suddenly becomes confused. It adds that you should not drive them yourself, but ask someone to drive or call an ambulance, and bring their medicines. For someone with a suspected urinary infection, the NHS says to call 999 or go to A&E if the person is confused, drowsy or has difficulty speaking.

For stroke-type features, the NHS cervical spondylosis page lists a drooping face, being unable to lift both arms and keep them there, and slurred or garbled speech as signs of a medical emergency, and the same principle applies to any new confusion with these features. Sudden severe headache, a stiff neck, a fit, a very high temperature, or someone who cannot be woken should always be treated as emergencies.

While waiting for help, the NHS suggests staying with the person, telling them who you are and where they are, using simple words and short sentences, and noting the medicines they take. It says not to ask lots of questions while they are confused and not to stop them moving about unless they are in danger.

• Confusion that appeared suddenly or over a few hours.

• Drowsiness, difficulty waking, slurred speech or a drooping face.

• A fit, a fall or a head injury.

• High temperature with shivering, or a very low temperature.

• Known diabetes with sweating, shaking or sleepiness.

• Others in the home also feeling unwell, which could point to carbon monoxide.

NICE CKS lists what an assessor covers in suspected delirium: the onset, nature and course of symptoms, the baseline mental and physical state, risk and precipitating factors, health conditions, medicines, alcohol and substances, sensory impairment, the social situation and, importantly, a history from relatives or carers. The family often notices that the person is not themselves long before a clinician can.

Examination includes vital signs, hydration and nutrition, signs of self-neglect and of chronic disease, and a search for the trigger. A cognitive screening test may be used and compared with earlier scores. CKS says targeted investigations are chosen according to clinical judgement, and that urgent hospital admission is considered depending on symptoms, likely cause, level of distress, risk of harm and the support available at home.

Tests follow the suspected cause: blood sugar, blood tests for infection or kidney and salt problems, urine testing, oxygen levels, an ECG and sometimes a scan of the brain. The NHS UTI page notes that for older people and people with dementia, changes in behaviour or confusion may be the only sign of urinary infection.

Treatment is for the cause, together with support. CKS recommends a safe, low-stimulation environment, reorientation, continuity of care, safe mobility and good sleep, with advice on de-escalation if the person is distressed. CKS says short-term antipsychotic medicines may be advised if someone is severely distressed or a risk to themselves or others, under specialist advice.

Slowly increasing forgetfulness or confusion over months is not an emergency in the same sense. The NHS says to see a GP if you are worried that you or a relative have gradually become more forgetful or confused: it may not be anything serious, but it is best to be checked. In older people it is sometimes a sign of dementia.

One practical reason for a GP review is that delirium can be superimposed on dementia. A change from someone's normal baseline, even in a person who already has memory problems, should be treated as new.