Fast or Irregular Heartbeat
Hypoglycemia can trigger cardiovascular reactions. Low levels of glucose in the blood cause your heart to beat rapidly and irregularly. This is usually because the body releases large quantities of epinephrine [2] into the bloodstream when hypoglycemia sets in. This hormone increases systolic blood pressure and decreases diastolic pressure, triggering an increase in heart rate.
This effect is usually resolved by taking in sugar to treat the low blood sugar. In some cases, severe alterations in heart rate can be very dangerous [3], even fatal.
Fatigue
Fatigue is a feeling of intense tiredness that can interfere with your ability to carry out normal functions. If your blood sugar is low, you may feel extremely tired. This is because your body depends on sugar for the energy it produces.
When your blood sugar drops below normal levels, your cells and muscles are not able to get enough sugar to convert into energy for you to use. The body also goes into a state where it begins to minimize energy [4] use so it can conserve the sugar remaining in your system. This is what causes fatigue.