Hello. I Have A Question. My 9 Yr Old Son

Hello. I have a question. My 9 yr old son had a strange incident last week. He was perfectly fine and one moment his hands started shaking, very quick heartbeat and blurry vision. The symptoms lasted for about half an hr. We went to the doctor next morning and she sent him for blood tests to hospital. The results came today and apparently everything is fine. What other tests could we run? It really worries me as these symptoms can mean something serious.