The symptoms of very high blood sugar include blurred vision; extreme thirst; lightheadedness; flushed, hot skin; and drowsiness, states WebMD. Other symptoms that occur when the body produces little or no insulin include rapid breathing, fast heart rate, weak pulse, strong fruity breath odor and loss of appetite or vomiting.
A person is considered to have severe high blood sugar when his blood levels are consistently above 350 milligrams per deciliter in adults and 240 milligrams per deciliter in children, according to WebMD. Many times the symptoms of severe high blood sugar levels, also known as hyperglycemia, are prefaced by symptoms of mild high blood sugar. These symptoms include fatigue, increased thirst, increase urination, weight loss and increased appetite.
Those who are diabetic can also check their blood glucose levels to check for high amounts of glucose in their system, according to the American Diabetes Association. High levels of sugar in the urine indicate issues with severely high blood sugar levels.
When symptoms reach an intense level where the person with hyperglycemia feels as though he may pass out, emergency medical assistance is necessary, according to Mayo Clinic. The person may be entering a diabetic coma. Severe nausea and vomiting, very dry mouth, shortness of breath and fruity mouth odors may also be indicators of ketoacidosis, a serious, life threatening issue that impacts those with high blood sugar, according to the American Diabetes Association.