Hypoglycaemia, or a "hypo", is an abnormally low level of glucose in your blood (less than four millimoles per litre). When your glucose (sugar) level is too low, your body doesn't have enough energy to carry out its activities. Hypoglycaemia is most commonly associated with diabetes, and mainly occurs if someone with diabetes takes too much insulin, misses a meal or exercises too hard. In rare cases, it's possible for a person who doesn't have diabetes to experience hypoglycaemia. It can be triggered by malnutrition, binge drinking or certain conditions, such as Addison's disease.