Hermione got sick in her second to last year of Hogwarts. It started as a cold that wouldn't go away. The unbreakable fever, a constant rawness in her throat, and her body ached where her glands were; around her neck and under her arms the most. She was always tired and had trouble focusing with the intensity that she was used to. She tried not to complain about it much. She went to see Madame Pomfrey a few times but the mediwitch just gave her all the normal tests and a few generic potions and sent her on her way.
Finally, when Hermione botched a relatively easy potion in potions class, Professor Snape asked her to stay behind.
"Miss Granger," he drawled, "you'll receive a zero for today." He waited for her to protest but she coughed demurely into her hand instead. Her coloring was off and he noticed her leaning into a desk for support. "How long have you felt ill?" he asked, his voice sharp.
"I'm fine, Professor," she said.
"Do not lie to me, girl," he barked.
"A few months, I suppose, from the very first moment of feeling unwell," she answered promptly, not wanting a late night detention to bog through.
"What does Pomfrey say?