What Causes Sudden Dizziness And Nausea Along With Body Tremors?

My son who is 26 years old, had a seizure or something last Saturday. He had worked all day outside and when to a family cook out. He became very dizzy and nautious and started to walk away as to not be sick in front of everyone. He got about 15 steps away and feel face first to the ground. His wife ran to him and rolled him over and his eyes were rolled back, his tongue was back in his throat and he was shaking a little. He got real stiff and she could only find a slow pulse. She sat him up and kept rubbing his face and he finally came back. Off course he would not go to the hospital and didn t remember anything. He showered and slept all day Sunday. He went to the walk in clinic yesterday. They took blood, a urine sample and did a Cat scan. We heard today the Cat scan showed and urine sample showed nothing. We are still waiting on results from blood work. He is normally very healthy and a workaholic. Please advise.