The men Jim discovers in the blockhouse number six, and all six (he says) seem to have been awakened from a drunken slumber. Silver is less given to drink and debauchery than the others, and here he seems sober and quick-thinking (as usual) immediately. But he is now worried — "desperate," he says — that he will have lost both the treasure and his life, which supports the notion that he has also been drinking.
Silver has several good reasons for despair. Of the eighteen other potential mutineers that he began with, he is down to five men; one of these is injured, another sick with fever. They have all begun to blame him for the fix they are in, and he knows that they will eventually overcome their fear of him enough to depose him and perhaps kill him. He and they believe — until Jim tells them otherwise — that Hands and O'Brien have taken the ship and left everyone on the island marooned. Finally, Silver cannot understand why Dr. Livesey has agreed to the "treaty" and handed over the stockade, supplies, and treasure map, so he is deeply suspicious.
Note that Livesey believes that George Merry and young Dick have contracted their fever from breathing the foul swamp air ("bad air" being a literal translation of the contraction in Italian for mala aria); it was not until later in the eighteenth century that science began to realize that mosquitoes and not the air itself caused the disease. And, in actuality, there was no effective treatment for either malaria or yellow fever in Livesey's time. Both were sometimes fatal, sometimes not.
