Causes of Hypoglycemia

In people taking certain blood-glucose lowering medications, blood glucose can fall too low for a number of reasons:

• meals or snacks that are too small, delayed, or skipped
• excessive doses of insulin or some diabetes medications, including sulfonylureas and meglitinides (Alpha-glucosidase inhibitors, biguanides, and thiazolidinediones alone should not cause hypoglycemia but can when used with other diabetes medicines.)
• increased activity or exercise
• excessive drinking of alcohol

source: http://diabetes.niddk.nih.gov/dm/pubs/hypoglycemia/index.htm