Final answer:
A 45-year-old insulin-dependent diabetic patient experiencing lightheadedness, weakness, and sweating is likely suffering from hypoglycemia, caused by low blood glucose levels.
Step-by-step explanation:
The 45-year-old patient with insulin-dependent diabetes mellitus who is experiencing lightheadedness, weakness, and sweating is most likely undergoing a hypoglycemic episode. Hypoglycemia occurs when blood glucose levels fall too low, which can happen if a diabetic patient takes too much insulin or does not eat enough to keep their blood sugar level stable. It is important for diabetic patients to manage their insulin dosages carefully and to carry a source of quick sugar such as candy or glucose tablets to counteract hypoglycemic events when they occur.