TSH (or thyroid stimulating hormone) is a measure of thyroid function. With any measurement, it's very important to know the units being used. For instance, 100mph is not the same as 100kph. For that matter, 6 inches is not the same as 6 feet, right? Most laboratories use equipment that allows for a normal reference range for TSH of 0.4-4.5mIU/L. If that's the case for your lab, then your 4.01 is normal. Some labs use 4.0 or less as an upper limit of normal, in which case, your 4.01 would be abnormal.
Regardless, lightheaded is not one of the cardinal symptoms of hypothyroidism, which is usually typified by fatigue, tiredness, exhaustion, weight gain, constipation, cognitive impairment, cold intolerance, etc. Lightheadedness could be a cerebellar (brain) issue or it could be due to low blood pressure, in and of itself, or due to anemia (low blood) or dehydration.
Best to get your family physician involved to determine what's going on. Good luck!
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