Turns out, Nix just couldn't bring himself to get out of bed.
"I just didn't want to wake up," Nix said. "I just felt so bad."
It didn't take long for Nix, the Irish or his teachers to figure out he had the flu.
"They knew something was wrong," Nix said. "If you don't see me smiling and laughing and joking around, then something's wrong with me."
Nix spent the next two days in the infirmary, getting medication round the clock -- "they woke me up at 4 a.m. just to get more meds," he said -- in an effort to get him healthy in time to play against Pittsburgh on Saturday.
When gameday arrived, Nix told Kelly that he wasn't ready to play, saying he wasn't even "70 percent." Kelly agreed, and said the Irish would only use him in an "emergency situation."
Well, it was an emergency situation. Kona Schwenke hurt his shoulder, and Nix went in the game.
The way Kelly tells it, Nix was fighting to get in. "He wanted to get in there and help his team."
The way Manti Te'o tells it, Nix was champing at the bit. "Louis has a lot of heart. He loves his team and he loves to win. There's no stopping him from getting on the field."
The way Nix tells it, he was more of a reluctant warrior: "They threw me out there and I did the best I could. Me, I'm all for the team. If I need to get out there, throw me in the fire. I don't care."
Understandable, Nix struggled with his conditioning. Usually on the field for five or more plays in a row at a time, he came out after every third play. But he was a big reason why Ray Graham and the Pitt ground game ground to a halt in the fourth quarter and overtime. As much as Nix is known for his goofy side and his "Chocolate News" videos on YouTube, he's a huge -- literally and figuratively -- part of Notre Dame's defense.
"When he got in there, he played very well," Kelly said. "He played really gutsy. He would come over to the sideline, and you could tell he was not feeling very well. But it was just a gutsy performance from a kid that was sick all week."