Applejack paced back and forth in her room. Did she have a reason not to tell Twilight about the situation? Not at that point, no. Did she have a reason to tell her about it? At that point, probably yes.
Maybe she should have known better. Or maybe not. It hadn't seemed like anything too noteworthy back then. It still didn't seem like anything particularly important. But was starting to feel it wasn't right.
Or maybe she was just worrying about nothing. Sweetie Belle had had it worse than her after the step, and Twilight had more than enough to deal with already. But it couldn't hurt to get herself checked, all things considered.
Maybe wait a few more days. It didn't feel like it was getting worse. If anything it was getting better, and it might pass fully. It had probably been a dumb idea not to bring it up when it was bad, but that was in the past. No use dwelling on it too much.
And if it came up again she'd definitely tell Twilight all about it. Or maybe not Twilight. Maybe she'd go to a doctor first, or to Starlight. If Starlight was around, of course.
It was probably just a regular fever, messed up by the Behemoth. But that was probably worth bringing up to the researchers. Maybe not right then though, she had a busy schedule and she was already feeling better. They wouldn't find anything looking at her.
That was probably it then. And she'd already spent enough time thinking about it when she had things to do.