I have no expertise in neuropsychology. But since you requested I stop by your question, I will tell you that it is alot harder to have a sense of humor after a sleepless night. I happened to have just had one myself as I've been struggling with some wicked insomnia. But I press through it because my sense of humor is one of the primary things that has saved me in life. Keeps me laughing at myself, and provides me with alot of company which is so important.

"Our two minds .... One is an act of the emotional mind, the other of the rational mind. In a very real sense we have two minds, one that thinks and one that feels" (Daniel Goleman, Emotional Intelligence, Bloomsbury Publishing, London, 1996, page 8). This rational mind is also called the faculty of logic and reason. The Upanishads say that these two are opposite in nature. Modern psychologist also have observed it, but they are not very sure about it: "At the same time, reason sometimes clearly seems to come into conflict with some desires (even while not being in conflict with others) giving us the impression that reason is separate from emotion". http://en.wikipedia.org/wiki/Reason The emotional mind is connected with the sense of humor and appreciation of fine sentiments. The rational mind becomes inactive during sleep, gets rest, and acts in a balanced mode after awakening. After a night without sleep, it works dominantly against the emotional mind. However, such a state is not that bad. If there is a situation which should be judged from rationality avoiding emotions, the morning after a night without sleep is the best time.

A job at a dysfunctional company with heinous levels of overtime and no end in sight, under a nasty boss.