This book was out in paperback in the mid 1970s. My English teacher read us a chapter in class and it has been haunting me for decades. I remember only that the protagonist was living underground in a bunker where computers and tech did everything for him, woke him up, gave him food. He spent the day online I think. Everyone there had been told the atmosphere above ground was unbreathable. But something went wrong and he had to crawl above ground. When he got there, he found it had been a lie - and he could breathe. Any help would be SO appreciated. I would so like to read it to the end.