In the worst cases, forgetting a shot of long-acting insulin can cause hyperglycemia and ketoacidosis. When the body lacks insulin to use glucose, it starts burning fat for energy instead, a process that produces blood acids known as ketones which are poisonous to the body. When the levels of ketones become too high, Diabetic Ketoacidosis (DKA) is a real risk. Mostly occurring in people with type 1 diabetes, DKA is a very serious diabetes complication that requires immediate medical attention; it can  also affect people with type 2 diabetes. Other common symptoms of low insulin include: - Thirst - Excessive urination - Confusion - Drowsiness - Sleepiness - Tiredness - Fruity smell in your breath - Nausea - Loss of appetite - Dry skin - Fast heart rate