Today is World Diabetes Day, turning the spotlight on this silent killer of almost 5 million people worldwide each year.

In the U.S. alone, 25.8 million people suffer from diabetes, including 7 million people who don’t even know they have it. And the number is growing, with two million adults newly diagnosed every year.

While the most common complications of diabetes, such as heart attack and stroke, can be years in the making, other severe complications can come on suddenly and may even be mistaken for something as commonplace as the flu.

In this video, Deborah, a 57-year-old who didn't know she had type 2 diabetes, talks about how she was diagnosed with the disease. At first she went to her doctor for a sore throat, but was so sick she eventually went to the hospital. In fact, her blood sugar had soared to 10 times what it should have been, and she began t to slip into a diabetic coma. She woke up in the intensive care unit.

Fortunately, Deborah recovered to tell her story, but not all people are so lucky.

Uncontrolled high blood sugar can cause both diabetic ketoacidosis and diabetic hyperosmolar syndrome, both of which can lead to a diabetic coma, which can be fatal.

“This state is a life-threatening emergency,” said Spyros Mezitis, MD, PhD, an endocrinology consultant and clinical investigator at Lenox Hill Hospital in New York City.

Diabetic hyperosmolar syndrome is more often seen in type 2 diabetics, which is by far the most common form of the disease. Diabetic ketoacidosis is more common in type 1 diabetics.

With diabetic hyperosmolar syndrome, your body tries to get rid of excess blood sugar by increasing urine output. This can lead to severe dehydration which, in extreme cases, leads to seizures, coma, or even death.

In diabetic ketoacidosis, a lack of insulin causes the body to burn fat, leading to a toxic build-up of acids called ketones in the blood.

Either way, the symptoms are similar and may be dangerously misleading.

“Patients become sluggish. They feel out of it. They become tired. Their muscles are aching,” said Dr. Mezitis.

People with diabetes and the flu may be at an even higher risk of falling into a diabetic coma as an infection (either influenza or something else), can cause blood sugar levels to spike.

“In a diabetic who’s not controlled, who’s not taking insulin correctly, they’re not compliant [with their medication], the sugar goes up fast and on top of that if he or she has the flu, you can have serious trouble with hyperosmolar syndrome,” Dr. Mezitis says.

How to avoid such a life-threatening crisis?

Watch for diabetes symptoms and get tested if you're at risk. Symptoms can include urinating a lot (particularly if you have to get up at night to go) or severe thirst, although many people have no symptoms at all. (Ask your doctor is you're at risk and have your blood sugar tested.)

And if you have been diagnosed with type 2 diabetes, make sure you keep your blood sugar under control by eating right, exercising, and taking medication if necessary. People with type 2 can take pills or injections of insulin or other drugs to control blood sugar. (People with type 1 have fewer options and need to take insulin to survive.)

For people at risk of type 2 diabetes, exercise may be the single best way to avoid diabetes, or at least avoid the complications. In this video, one man with a family history of the disease started running regularly in his 40s and so managed to delay his diagnosis until he was in his mid 60s. That greatly reduced the chances of developing any complications.

In addition to lifestyle interventions, many people with type 2 diabetes take medications to control their blood sugar and, in some cases, even insulin to help get glucose out of the bloodstream and into the fat where it’s stored until needed.

And get your flu shot every year. That goes for diabetics and non-diabetics alike.

According to the U.S. Centers for Disease Control (CDC), the flu shot can reduce your risk of getting sick by about 60%.

The CDC recommends that all people over the age of 6 months get vaccinated, especially those with compromised immune systems, such as people with diabetes, as well as people over the age of 65.