Leon was probably not feeling well to begin with. But he ignores it because he takes training very seriously. His pokemon can tell he’s not well and wants him to rest, but he ignores them. Until he breaks down on the treadmill, unable to get up because he’s so weak.
Charizard helps him to the sofa so he can lay down. He calls Raihan to come by and help. He, of course, does.
Leon has a fever and is throwing up. His body is sore and he’s just exhausted. He spends most of his time asleep on the couch. Raihan doesn’t want to take him upstairs to his bedroom because if he knows Leon, and he does, he’ll get up and try to go down the stairs and hurt himself.
Raihan just makes sure he rests, keeps his temp down, and makes sure he drinks plenty of water. He hangs around Leon’s place, sleeping on the other sofa, and just watching Leon like a hawk. Surprisingly, Raihan is a very good caretaker.
Of course, as soon as Leon’s feeling better, he goes back to training. This annoys Raihan, but there’s no changing this about his rival. He takes his work very seriously.
Of course, Leon thanks him and buys him lunch afterwards.