Diabetes Mellitus is a disorder characterized by high blood sugars (hyperglycemia). It is diagnosed by having sugars that are > 126 mg/dl in the morning before eating, or > 200 mg/dl after meals. Mild low blood sugars (hypoglycemia) are sugar levels 50-70 mg/dl. Significant low sugars are sugars < 50 mg/dl. Symptoms of low blood sugars actually occur due to the sympathetic response in the body to the low sugar, and include anxiety, weakness, tremor, perspiration, or palpitations.
Significantly low sugars (<50 mg/dl) can have several causes. In a patient who already has diabetes, the most likely cause is that it is a side effect of a medication. In a patient without diabetes, significant hypoglycemia is otherwise very uncommon.
There is some evidence that rarely patients with pre-diabetes or very early diabetes may have significant low sugars after meals. This is presumably due to a delayed but then inappropriately strong insulin response to the rapid rise in glucose after a meal. Therefore, patients who have significant hypoglycemia (sugars < 50 mg/dl) may want to discuss screening for diabetes with their doctor.