This is because there are so many factors that can contribute to hypoglycemia
-- stress, hormones, activity, what foods
, and a myriad more. So sometimes the hypoglycemia doesn't happen when you are being tested. But it is worth asking your doctor to check for. The symptoms are exactly what you describe -- light-headed feeling, nausea sometimes, hunger sometimes, dazed feeling, fatigue, headache, hot or cold spells with no reason, unexplained yawning.