Diabetics with high sugar levels experience symptoms such as increased thirst, difficulty concentrating, blurred vision and fatigue, according to WebMD. High blood sugar levels, also known as hyperglycemia, can also cause headaches, frequent urinating and weight loss.
Severe symptoms can occur in diabetics who have ongoing high blood sugar levels, explains WebMD. Some people may experience nerve damage that causes loss of hair on the lower extremities; erectile dysfunction; or painful, cold or insensitive feet. Vaginal and skin infections, as well as stomach and intestinal problems that produce diarrhea or chronic constipation, can occur when blood sugar levels are high. Persistent high blood sugar levels in diabetics can cause damage to the kidneys, eyes and blood vessels and diminish the body's ability to heal cuts and sores.
High blood sugar levels can occur when diabetics skip insulin or oral glucose-lowering medications, eat too many carbohydrates or do not exercise sufficiently, according to WebMD. However, strenuous physical activity when insulin levels are low and blood sugar levels are high can increase the levels even more. Infections, illness and stress also affect blood sugar levels in diabetics. Patients affected by hyperglycemia should ensure they are adhering to a diabetic diet, taking medications as directed and consulting with a physician when they get unusually high blood glucose readings repeatedly.