Answer: a major depressive disorder
Explanation:
Depressive disorders are psychological mood, where an individual worries or think beyond the normal, especially sad thoughts from a very dampened mind. Depression starts in the mind and it's all emotional, they are various categories of them but when the situation is hard to come out from by the individual alone, and he would need a therapist then it's a major depressive disorder. What causes this is vast but all relates to what concerns people and their needs. This is what Norby is suffering from.