Suppose I have a halfling that's multiclassing as a fighter/thief and has achieved 2nd level in both classes. This character has the misfortune of being struck by a wight and loses a level.
What happens here? Is the character now level 1/1, or do they become a level 1 fighter and a level 2 thief? If they lose a level in only one class, how do you determine which one?