Lethargy is a common symptom of that disease.

As I have mentioned somewhere in these incoherent memoirs, the outbursts of passionate energy when he performed the remarkable feats with which his name is associated were followed by reactions of lethargy during which he would lie about with his violin and his books, hardly moving save from the sofa to the table.

Eating too many carbs before a run, if your body isn't used to it yet, could lead to lethargy.