Ted chiang — understand

A layer of ice; it feels rough against my face, but not cold. I've got nothing to hold on to; my gloves just keep sliding off it. I can see people on top, running around, but they can't do anything. I'm trying to pound the ice with my fists, but my arms move in slow motion, and my lungs must have burst, and my head's going fuzzy, and I feel like I'm dissolving —
I wake up, screaming. My heart's going like a jackhammer. Christ. I pull off my blankets and sit on the edge of the bed.
I couldn't remember that before. Before I only remembered falling through the ice; the doctor said my mind had suppressed the rest. Now I remember it, and it's the worst nightmare I've ever had.
I'm grabbing the down comforter with my fists, and I can feel myself trembling. I try to calm down, to breathe slowly, but sobs keep forcing their way out. It was so real I could feel it: feel what it was like to die.
I was in that water for nearly an hour; I was more vegetable than anything else by the time they brought me up. Am I recovered? It was the first time the hospital had ever tried their new drug on someone with so much brain damage. Did it work?
The same nightmare, again and again. After the third time, I know I'm not going to sleep again. I spend the remaining hours before dawn worrying. Is this the result? Am I losing my mind?
Tomorrow is my weekly checkup with the resident at the hospital. I hope he'll have some answers.
I drive into downtown Boston, and after half an hour Dr. Hooper can see me. I sit on a gurney in an examining room, behind a yellow curtain. Jutting out of the wall at waist-height is a horizontal flatscreen, adjusted for tunnel vision so it appears blank from my angle. The doctor types at the keyboard, presumably calling up my file, and then starts examining me. As he's checking my pupils with a penlight, I tell him about my nightmares.

"Did you ever have any before the accident, Leon?" He gets out his little mallet and taps at my elbows, knees, and ankles.
"Never. Are these a side effect of the drug?"
"Not a side effect. The hormone K therapy regenerated a lot of damaged neurons, and that's an enormous change that your brain has to adjust to. The nightmares are probably just a sign of that."
"Is this permanent?"
"It's unlikely," he says. "Once your brain gets used to having all those pathways again, you'll be fine. Now touch your index finger to the tip of your nose, and then bring it to my finger here."
I do what he tells me. Next he has me tap each finger to my thumb, quickly. Then I have to walk a straight line, as if I'm taking a sobriety test. After that, he starts quizzing me.
"Name the parts of an ordinary shoe."
"There's the sole, the heel, the laces. Um, the holes that the laces go through are eyes, and then there's the tongue, underneath the laces…"
"Okay. Repeat this number: three nine one seven four — "
" — six two."
Dr. Hooper wasn't expecting that. "What?"
"Three nine one seven four six two. You used that number the first time you examined me, when I was still an inpatient. I guess it's a number you test patients with a lot."
"You weren't supposed to memorize it; it's meant to be a test of immediate recall."
"I didn't intentionally memorize it. I just happened to remember it."
"Do you remember the number from the second time I examined you?"
I pause for a moment. "Four zero eight one five nine two."
He's surprised. "Most people can't retain so many digits if they've only heard them once. Do you use mnemonic tricks?"
I shake my head. "No.