My son faints and his eyes rolled off after jogging. Please help.

Hi doctor,

My son and I went for a jog. We used to run in our regular route but had not done it for about a week and a half. We would usually run to point A, stop for a few seconds, catch our breath, do a brisk walk, and run back home. However, when we reached point A, we stopped to catch our breathe, my son stated that he was feeling a bit nauseous. He usually sits on a railing when we reached that point. He was sitting when he said that. Shortly after saying he was nauseous, he said that he was feeling to faint. About five seconds after he collapsed on me. When I looked at him, he was delirious for a few seconds then his eyes rolled back in his head. He started gasping for air and had slight muscle convulsions. He seemed unable to breathe. It lasted about 20 to 30 seconds then he was completely out. He stopped moving and seemed like he was asleep. I kept calling him and lightly tapping his cheek to wake him. When he got up, he gasped again and called out to me. His eyes were still rolling back a bit, but he seemed more conscious than before. At this time, someone came to assist and helped me stretch out his legs. I kept telling him to take deep breaths, and when he looked conscious, he started crying and saying that he was in pain. When I asked where it was paining he pointed to his butt and hamstring. So I automatically thought it was a cramp and started rubbing the tendon by his ankle and calf. After a few seconds, he said it had eased a bit. He remained on the pavement for about 15 minutes before I asked him if he could get up. He still looked nauseous and stated that his leg was still hurting a lot but only when he tried to move.

My son is involved in football and swimming and is usually very active. However, due to the restrictions of COVID-19, he has been active when with me and inactive while with his grandparents. It is usually one week with me and one week with them. Over a few months, he also gained a little weight. Kindly advise.