Eben is a fairly severe asthmatic, a condition that isn't helped by the cold. He's always kept an inhaler on him at all times and will typically end up using it after extremely stressful or physically strenuous events. With the town under attack, 'extremely stressful' and 'physically strenuous' have become regular occurrences, and somewhere along the line, he lost his inhaler. Asthma attacks have to be avoided, or he just does his best to ride them out until he can get another, if he can.
The vampire disease, along with granting him the strength, speed and durability to save the last survivors of Barrow, cured him of his asthma problem.