In the ten-fifteen minutes that it took Sora to come back to the computer, Riku had finally fallen into a kind of sleep, at least deep enough that the to little 'pings' on his computer didn't wake him up.
That was why when his alarm went off in an hour he pulled himself out of bed and went to meet with a couple of his and Sora's people who wanted to show him some of their ideas, which he kept and made copies of to show to Sora on the weekend.
If you asked him, he wasn't 'sick.' He was 'just a little stressed' and was 'fine' really, he just needed to tough it out and get used to being back at school. He blamed the coughing on the cold, it was irritating his lungs. He blamed the color high in his otherwise pale cheeks on the wind. He blamed the glassiness of his eyes on the fact that he'd been using the computer a lot without his glasses.
By the time he finally made it back to his room, deciding against dinner because the thought of food was suddenly appeasing, Riku barely had his jacket off before he collapsed onto his bed and fell asleep again.