A deficiency of glucose in the blood – the normal range being 3.5–5.5 mmol/l (see DIABETES MELLITUS). It most commonly occurs in diabetic patients – for example, after an excessive dose of INSULIN and heavy exercise, particularly with inadequate or delayed meals. It may rarely occur in non-diabetic people, for example, in very cold situations or after periods of starvation. Hypoglycaemia is normally indicated by characteristic warning signs and symptoms, particularly if the blood glucose concentration is falling rapidly. These include anxiety, tremor, sweating, breathlessness, raised pulse rate, blurred vision and reduced concentration or even just the external appearance of intoxication by alcohol, leading – in severe cases – to unconsciousness. Symptoms may be relieved by taking some sugar, some sweet biscuits or a sweetened drink. In emergencies, such as when the patient is comatose (see COMA), an intramuscular injection of GLUCAGON or intravenous glucose should be given. Early treatment is vital, since prolonged hypoglycaemia, by starving the brain cells of glucose, may lead to irreversible brain damage.