Low blood glucose, also known as low blood sugar or hypoglycemia, is when a person’s blood glucose levels fall below 70 mg/dL. Symptoms of hypoglycemia can set in quickly and can include shakiness, anxiety, cold sweats, confusion, fast heartbeat, dizziness, hunger, sleepiness, blurred vision, headaches, exhaustion, and even seizures or loss of consciousness.

Source:
http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hypoglycemia-low-blood.html