Can you fast if you have hypoglycemia?

Depends. It depends on the cause of hypoglycemia. Unless you actually have low blood sugar during periods of hypoglycemia, it's generally safe to not eat after midnight for a 8 am labs.
Depends on cause. For people with a post-prandial hypoglycemia (blood glucose drops after eating) that is related to Insulin resistance, there should be little danger in fasting. People who have a tumor that produces Insulin or who take Insulin but do not lower the dose before a fast, the blood sugar could drop too low when fasting.
Hypoglycemia is rare. Symptoms include nervousness, sweating, hunger, anxiety, blurred vision, fatigue, fast heart rate, etc. -- however unless you have diabetes and are on Insulin or other medication, have renal or liver disease, cancer or prior stomach surgery -- then true hypoglycemia neveer occurs in human beings. If it a very frequently and incorrectly made diagnosis.
Please define. Hi. Please define hypoglycemia. If you're not taking diabetes drugs, true pathological hypoglycemia is vanishingly rare. Do you become confused, lose consciousness, have a seizure? If not, there is a popular self-diagnosis of "hypoglycemia" that isn't real. So, unless you have real, pathological hypoglycemia, you're fine fasting for as long as you want. If you have real hypogly, see endocrinologis.