Chapter 17, what situation has Yossarian in during this chapter and is he have any responsibility for this situation given the circumstances?

I'm not sure about which circumstance you are referring to. Quite a few things happen in that chapter.

The end of the chapter, sorry!

Yossarian knows so much about fatal disease that he begins to wonder whether he can recognize the symptoms of his own fatal illness and if the doctors in the hospital can save him. Daneeka refuses to sympathize with Yossarian and to give orders for Yossarian to be grounded. At first, he denies that he even has the power to do this, but when Yossarian says that Major Major confessed this in a ditch to him, Daneeka points out the futility of performing his action--Catch-22.

Daneeka then resumes his pathetic posturing and tells Yossarian to at least finish five missions first before asking for help. As Yossarian leaves, he tells the sick Daneeka that he has Ewing's tumor and continues to worry when he will fly his final, fatal mission.