It's strange, but Becca doesn't know what exactly made Tommy look like that. Even Tommy sleeps with his back to him, which is rarely done unless Tommy has a problem or something makes him look bad mood.
But Becca didn't ask. They were too stiff and cold to ask each other if something really happened. The two even chose to remain silent until the atmosphere melted.
As the night wore on, Becca couldn't sleep while beside her Tommy was asleep. Possible. Actually he wasn't sure if Tommy was asleep. Because he didn't feel Tommy's movement.
Finally, Becca ends up not sleeping. She chose to keep her eyes wide open until early in the morning, sleepiness even came, but she couldn't sleep right away because her husband was going to work.