Shinjiro isn't sure how long he's been sitting here with you for.
The television, which is still playing his favorite cooking show, has somehow become white noise, as he becomes more focused on keeping himself awake.
It's only now that he realized just how tired that he was. Maybe it was the feeling of your arms wrapped around him like a warm blanket, or your body acting as a cushion to rest his head on that caused him to relax enough to not be kept up by constant thinking.
Or maybe he really was just that tired. He doesn't bother trying to figure it out, since it'd take too much energy. He buries his face into your chest, his eyes tired from looking at the screen for such a long period of time. He had no reason to keep watching for so long, anyway.
He doesn't really want to go to sleep just yet. He can't feel your warmth around him in his dreams, can he? Besides, he doesn't actually know if you'd want him falling asleep on you right now.