I think the Bush crowd and Rove gave him the old "you are the standard bearer for all of us and you must do what ever can be done to win" line.  I saw a hint on CounterPunch that he may have gotten bad news from his oncologist.  With the direction and conduct of the campaign, the likely outcome of the election and the probable resultant depression for JSM the prognosis is poor.

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."