An excerpt from Tuesdays with Morrie:
“You know how I’m going to die?” he said. I raised my eyebrows. “I’m going to suffocate. Yes. My lungs, because of my asthma, can’t handle the disease. It’s moving up my body, this ALS. It’s already got my legs. Pretty soon it’ll get my arms and hands. And when it hits my lungs … He shrugged his shoulders. “… I’m sunk.” I had no idea what to say, so I said, “Well, you know, I mean … you never know.” Morrie closed his eyes. “I know, Mitch. You mustn’t be afraid of my dying. I’ve had a good life, and we all know it’s going to happen. I maybe have four or five months.” Come on, I said nervously. Nobody can say.
What does I'm sunk mean?