Among people with diabetes, dangerously low blood sugar levels often trigger warning signs such as heart palpitations and double vision.

But for a small minority, these signs are not present and a person may feel perfectly fine – up until the point where he suddenly collapses, losing consciousness or having a seizure.

The phenomenon is known as impaired hypoglycaemia awareness.

It has been extensively studied among Type 1 diabetics, but is less well understood among people with the Type 2 version.

This is despite the fact that Type 2 diabetes is far more common, said Dr Teh Ming Ming of the Singapore General Hospital's endocrinology department, who is studying the problem.

“Type 2 diabetes patients are a much more diverse group,” he said. “That’s what makes studying them more challenging.”

While people with Type 1 diabetes cannot produce insulin, which is needed to control blood sugar levels, those with Type 2 diabetes cannot use insulin effectively.

Dr Teh’s research involving 370 people, who were studied between August and December 2015, found that on average, about 15 per cent of Type 2 diabetics are affected by the problem.

“It’s extremely distressing because you can easily get into serious trouble if you are not treated in time,” he said. “One theory behind why it happens is that the brain gets desensitised to low blood sugar.”

The study focused on people who were being treated with insulin, meaning that their conditions were more serious.

Dr Ben Ng, an endocrinologist at Mount Elizabeth Novena Hospital, said that the problem of impaired hypoglycaemia awareness is likely to be more common than most people think, and that he encounters it “nearly on a daily basis”.

“Many people with diabetes tend to focus on high sugars, and try to lower their levels, but very few actually worry about the dangers when their glucose levels start to fall,” he said.

Dr Teh said that he hopes to use these findings to raise awareness about the issue, especially among primary-care doctors such as general practitioners.

He is also planning a follow-up study in which participants will have to write down all the times they felt low blood sugar symptoms over a four-week period.

He recommends that all those who think they might have the problem check their blood sugar levels regularly and keep track of any symptoms that they might experience.

“Even checking once a day is a good start, and it’s a good idea to take measurements at different times of the day,” he said.

Dr Ng added that it is important for family members to learn to recognise the early signs of hypoglycaemia and respond appropriately.

“This is because in severe cases... the individual is unable to help himself,” he said. “It is important that someone nearby, or his caregiver, knows how to recognise and treat the symptoms... before further complications develop.”