Yossarian and Dunbar decide to play a practical joke on Nurse Duckett. As she is tending to him one day, Yossarian places his hand underneath her skirt, and when she jumps away, Dunbar does the same. This “horsing around” causes Dunbar to fall and hit his head. A doctor comes by to ask if Yossarian is crazy, and Yossarian responds that he is. He begins going to therapy session with a psychologist, Major Sanderson.
This “practical joke” would nowadays be considered sexual harassment. During the Second World War, however, there was quite a bit of misogyny ingrained in the culture of the military, with mostly men away overseas, and groups of women tending to those men in their capacities as nurses or aides.
Sanderson appears to have as many, if not far more, anxieties as the patients he is supposed to help. Yossarian recounts a dream that Dunbar had, about a fish, and the Major interrupts to complain about how lonely and difficult his job as a therapist is—he believes that Yossarian does not empathize with him enough.
Another irony: Sanderson, who is supposed to help tease out the anxieties of his patients, has enough anxieties for a whole boatload of psychologically-battered soldiers. Sanderson tends to use therapy sessions as occasions to voice his own demons.
Sanderson asks if Yossarian has real and interesting sex dreams, and when Yossarian says his fish dream is a sex dream, and is actually Dunbar’s dream, Sanderson believes that Yossarian has invented an imaginary friend name Dunbar. This excites Sanderson. It is revealed that Sanderson has the patient information for A. Fortiori, who he thinks Yossarian really is. When Yossarian tries to tell him otherwise, Sanderson believes this only to be further proof of Yossarian’s insanity.
The name “A. Fortiori” is a pun on a Latin phrase, “a fortiori,” which is a logical term denoting a stronger argument that outweighs any other, supplemental arguments. Here, of course, Sanderson believes that Yossarian is really Fortiori and only thinks that he's “Yossarian” out of some form of psychological delusion.
Dobbs comes to visit Yossarian in the hospital. He wants to talk about the plan to murder Colonel Cathcart. Yossarian tells Dobbs to quiet down, since he worries someone will hear of the plan. The chaplain enters and tries to speak to Yossarian; Yossarian tells the chaplain, who appears stressed, that he ought to check into the hospital for a spell, to recover.
Dobbs once again asserts that he is crazy enough to kill Cathcart, while Yossarian, who is ostensibly in the hospital being looked over for mental illness, takes the rational view that killing their superior officer would be a bad way out of their combat missions.
Sanderson, in his meetings with Yossarian, grows angrier and angrier. He believes Yossarian has not “adjusted” to war, that he has never come to terms with the fact that the enemy is trying to kill him. When Yossarian agrees—thinking this a normal way to behave—Sanderson views it as a final proof of Yossarian's insanity and anti-social behavior.
Yossarian, of course, believes that war itself is insane, therefore adjustment to war would make the soldier insane as well. Many soldiers in the novel bear this out, including Hungry Joe, who is so accustomed to war only the thought of more combat missions will ease his troubled dreams.
But Sanderson also still believes that Yossarian is really A. Fortiori, the other soldier—thus Fortiori is sent home on account of mental illness, and Yossarian, whose leg wound has turned out less serious than anticipated, is released back into the group with Dunbar, who has also recovered from his head injury during the Nurse Duckett incident.
Not a catch-22, but an instance of plain poor luck. Yossarian does manage to get his “insane” diagnosis, but that discharge is applied to A. Fortiori. Dunbar always seems to appear in the hospital with Yossarian, perhaps out of a sense of camaraderie, or perhaps merely out of coincidence.
Yossarian speaks with Doc Daneeka, who is worried that, if the Germans surrender too quickly, before Japan is defeated, he will be sent to the Pacific after all, with all its exotic diseases. Yossarian explains to Daneeka that he was diagnosed as crazy at the hospital, but that Foriori was accidentally sent home in his place by Sanderson. Daneeka is unmoved—if Yossarian is crazy, well, who but a crazy man could continue to fly missions against the enemy?
Once again, a fear of the Japanese is noted. Apart from the diseases present in the South Pacific, Daneeka implicitly fears what was called the ruthlessness of the Japanese army, which was said not to take prisoners, and to behave with cold, calculating cruelty against American men.