Before developing a diabetic coma, you'll usually experience signs and symptoms of high blood sugar or low blood sugar.

High blood sugar (hyperglycemia)

If your blood sugar level is too high, you may experience:

• Increased thirst
• Frequent urination
• Fatigue
• Nausea and vomiting
• Shortness of breath
• Stomach pain
• Fruity breath odor
• A very dry mouth
• A rapid heartbeat

Low blood sugar (hypoglycemia)

Signs and symptoms of a low blood sugar level may include:

• Shakiness or nervousness
• Anxiety
• Fatigue
• Weakness
• Sweating
• Hunger
• Nausea
• Dizziness or lightheadedness
• Difficulty speaking
• Confusion

Some people, especially those who've had diabetes for a long time, develop a condition known as hypoglycemia unawareness and won't have the warning signs that signal a drop in blood sugar.

If you experience any symptoms of high or low blood sugar, test your blood sugar and follow your diabetes treatment plan based on the test results. If you don't start to feel better quickly, or you start to feel worse, call for emergency help.

Blood sugar that's either too high or too low for too long may cause various serious conditions, all of which can lead to a diabetic coma.

• Diabetic ketoacidosis. If your muscle cells become starved for energy, your body may respond by breaking down fat stores. This process forms toxic acids known as ketones. If you have ketones (measured in blood or urine) and high blood sugar, the condition is called diabetic ketoacidosis. Left untreated, it can lead to a diabetic coma.

Diabetic ketoacidosis is most common in type 1 diabetes but sometimes occurs in type 2 diabetes or gestational diabetes.

• Diabetic hyperosmolar syndrome. If your blood sugar level tops 600 milligrams per deciliter (mg/dL), or 33.3 millimoles per liter (mmol/L), the condition is called diabetic hyperosmolar syndrome.

Severely high blood sugar turns your blood thick and syrupy. The excess sugar passes from your blood into your urine, which triggers a filtering process that draws tremendous amounts of fluid from your body. Left untreated, this can lead to life-threatening dehydration and a diabetic coma. About 25 to 50 percent of people with diabetic hyperosmolar syndrome develop a coma.

• Hypoglycemia. Your brain needs glucose to function. In severe cases, low blood sugar may cause you to pass out. Hypoglycemia can be caused by too much insulin or not enough food. Exercising too vigorously or drinking too much alcohol can have the same effect.

Anyone who has diabetes is at risk of a diabetic coma, but the following factors can increase the risk:

• Insulin delivery problems. If you're on an insulin pump, you have to check your blood sugar frequently. Insulin delivery can stop if the pump fails or the tubing (catheter) is twisted or falls out of place. A lack of insulin can lead to diabetic ketoacidosis.
• An illness, trauma or surgery. When you're sick or injured, blood sugar levels tend to rise, sometimes dramatically. This may cause diabetic ketoacidosis if you have type 1 diabetes and don't increase your insulin dosage to compensate.

Medical conditions, such as congestive heart failure or kidney disease, also may increase your risk of diabetic hyperosmolar syndrome.

• Poorly managed diabetes. If you don't monitor your blood sugar properly or take your medications as directed, you'll have a higher risk of developing long-term complications and a diabetic coma.
• Deliberately skipping meals or insulin. Sometimes, people with diabetes who also have an eating disorder choose not to use their insulin as directed with the hope of losing weight. This is a dangerous, life-threatening practice that increases the risk of a diabetic coma.
• Drinking alcohol. Alcohol can have unpredictable effects on your blood sugar. Alcohol's sedating effects may make it harder for you to know when you're having low blood sugar symptoms. This can increase your risk of a diabetic coma caused by hypoglycemia.
• Illegal drug use. Illegal drugs, such as cocaine and ecstasy, can increase your risk of severe high blood sugar levels and conditions linked to diabetic coma.

Left untreated, a diabetic coma can lead to:

• Permanent brain damage
• Death