[Florence] glanced up, apprehensively, through the kitchen window. [...] They had no right to put those Sputniks up there to spy on people. (1.6)
People like Florence aren't sure why they're afraid—all they know is that they're quaking in their boots 24/7. While it's easily to laugh at Florence's paranoia and hilariously 1950s lack of knowledge about satellites, it's hard to say that her fears are unfounded given what's about to go down.
Of one thing he was certain, if Mark expected it to come, it would probably come. His brother was no alarmist (1.74)
Randy has heard plenty of people wax paranoid about an impending nuclear holocaust, and never once has it scared him. But Mark was never the one issuing those warnings in the past. From a trustworthy source, this is one scary possibility indeed.
[Alice] had small fear of death, and of man none at all, but the formlessness of what was to come overwhelmed her. (2.38)
Even if you somehow aren't afraid of the nuclear apocalypse (good luck with that) you're still probably afraid of the societal collapse that would inevitably follow. In fact, you'd be certifiably insane if you weren't —not that there'll be anyone left to do the certifying when everything's said and done.
Randy held [Lib], crushed her, strangely without any passion except fear for her. (3.141)
Scary situations become even scarier once people you love get involved. You're not just worrying about your safety anymore; you're worried about theirs, too.
"You see, all their lives [...] they've lived under the shadow of war—atomic war. For them the abnormal has become normal." (4.147)
Peyton and Ben Franklin haven't even reached puberty, yet they're handling the nuclear attack with more grace and courage than the adults. Helen attributes to them living their whole lives in the atomic age. They have no idea things were ever different.
Realization did not come all at once. It could not, for his mind refused to assimilate it. (5.190)
Some people, like Edgar Quisenberry, are so trapped in their bubbles that they're not afraid even after the bombs start falling. For them, it'll take a few more mushroom clouds for those balloons to finally pop.
The guests were milling around in the lobby like first-class passengers on a liner that has stuck an iceberg, and that they suspect may founder at any moment. (5.83)
Ah yes—nothing like a Titanic metaphor to nail down the whole "We're all doomed!" vibe. What's particularly rough for these folks is that they're on vacation when the world ends. Imagine that. Hundreds of nukes rain down across the United States and you're not even afforded the dignity of watching it go down from your own bed,
"Not much I can do for cardiacs. [...] It's fear that kills 'em, and the worst fear is that they'll have a shock and not be able to reach the doctor." (5.109)
As it turns out, fear can do a lot more than give you the sweats—it can kill you. The risk is even greater when you have heart problems.
"No! No, I'm not going to carry a gun. I've spent too many years learning how to save lives to start shooting people now." (7.125)
It's easy to start fearing your fellow man in a situation like this—especially when you've just witnessed the scene of a gruesome murder, as Dan has here—but we think it's admirable that Dan stays true to his moral code. You've got to stick to something, right?
If a man kept busy enough [...] he could [...] forget the insidious, the invisible, the implacable enemy, but not forever. (8.50)
Of course, all our heroes' trials and tribulations could be for naught if an errant wind blows radiation in Fort Repose's direction. But that's not the kind of thing that Randy and co. can waste their time fearing. They'll worry about radiation once they've figured out how to survive until tomorrow.