Alum is an emotional state that is neither glum nor joyful. This leaves open a wide range of feelings, making alum a horribly imprecise and, therefore, not very helpful word.
To say that someone is alum imparts little more information than that he or she is alive. True, you do know that he or she is not glum or joyful, but he or she could be, for example, ecstatic, miserable, indifferent, frustrated, aroused or comatose.
Generally, you would describe someone as alum when you haven’t a clue what his or her emotional state is. Although, comatose is typically considerably easier to recognize than most of the other emotional states. Here’s a test to determine if the person is comatose: Try complimenting the person profusely. Next try insulting the person vilely. Finally, try violently jabbing him or her with a hat pin a few times. (It doesn’t have to be a hat pin. Any sharp, pointy object will do.)
If you get no reaction after the compliments, insults and hat pins, the person is either comatose or a civil servant. If you know he or she is not a civil servant then you can safely refer to the person as being comatose. In that case, it would be overly vague to refer to the person as alum.