Diabetes is a disease characterized by elevations in blood sugar (glucose). Insulin treatment reduces glucose levels, sometimes below normal levels. Extremely low levels of glucose can cause changes in mental function, seizures, and coma. Diabetic patients can usually sense early warning symptoms of low blood sugar, such as sweating, hunger, tremor, or fast heart rate. These warning signs probably depend on the release of adrenalin-like hormones. Unfortunately, some patients stop developing these warning signs, particularly after many episodes of low blood sugar. These people are more likely to have very low levels of glucose, which sometimes result in serious injury.