Symptoms of low blood sugar (hypoglycemia) include feeling shaky, having a fast heartbeat, sweating, feeling dizzy or weak, and having blurry vision. It can be caused by not eating enough food, taking too much insulin or diabetes medication, or being more active than usual. Symptoms come on suddenly. If blood sugar levels are not treated, a person may pass out or need medical help. To treat, check blood sugar levels and if low, eat glucose tablets, hard candies, fruit juice, or soda pop. Check blood sugar again after 15 minutes and treat again if still low.