My 13 y/o son is complaining of lightheadedness. He stated that he feels dizzy when he lays down, sits, etc. It doesn t always last for a long time but enough for him to come to me. He has a history or migraines and was diagnosed with a chiari malformation when he was 9. They said however that when he went through puberty (which he is going through now) that the chiari may not become a problem. He is currently not on any medications. Any ideas?
You need to check his pulse - is it strong and regular, or are there missed beats. Also, his BP should be measured when he is upright and when he is on the bed. Numerous conditions can cause dizziness, but the most relevant ones are rhythm disturbances of the heart, a high blood pressure, migraine, heat-related dizziness, deny Chat Doctor.  He needs a proper evaluation by a good physician, and perhaps, tests to determine if any of the above problems are present. Rarely, problems with the balancing organ of the inner ear may also cause these symptoms. If he has any ear problem history, please take him to ENT as well. Hope this helps without scaring you ... I am sure he will turn out to have a minor issue, most likely migraine. Best wishes.