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Snap awake = suddenly get awake?
Ventilator = electrical fan? Air conditioner?

Context:
The accident's power over him was diminishing, he said, as his ventilator sucked and hissed. He no longer snapped awake in the quiet hours, forced to confront, all over again, the fact that he had no sensation from the neck down. He didn't need to turn away when he was driven past the barn where he kept Buck, the thoroughbred horse from which he had been thrown in 1995, breaking his neck. But learning to live with his paralysis wasn't the same as resigning himself to it. "I've still never had a dream that I'm disabled," he said. "Never." He had vowed, controversially, to walk again by the age of 50. At the time, that deadline was three weeks away.
Comments  
Yes you have the correct meaning.
In this case I believe a "ventilator" is a medical device which "breathes" for a paralyzed person. They typically make "sucking and hissing" sounds.

Emotion: smile
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CJ, you are so cool to figure out that!
In the thread, " At the time, that deadline was three weeks away."

"At the time" refers to when Reech spoke "I've still never had a dream that I'm disabled," he said. "Never." ?
At the time (that he vowed he would walk before he was 50), he was about 49 years, 11 months, and one week old.

Emotion: smile
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I think "at the time" in this case means at the time when he was interviewed for the article you are reading.

It is quite likely that by the time to article was published three weeks would have passed. Because of this nearness to the deadline, the author probably felt it would be important to clarify.

Also, I believe that Reeves was quoted as vowing to walk again by age fifty numerous times. He was famous and it was quite a statement. He worked very hard to raise lots and lots of money and did all kinds of lobbying for changes in laws and funding streams. As that deadline drew nearer however, it became clear that medical science could not help him.

It doesn't look to me as though he repeated the vow to this interviewer. If he had, I'm assuming his words would have been repeated ver batim in quotation marks. At three weeks away from the deadline, I don't think I would have asked him about it if I had been the interviewer. Would you?
I don't get "deadline" either, because it seems to mean both:

1) The time of being 50 years old;

2) The time of his passing away.

Which one is correct?
Upon rereading the text, I retract my interpretation. Emotion: crying

It is as Guest says. At the time of the interview the deadline (of his being 50 years old) was three weeks away.

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