Harry Potter and the Prisoner of Azkaban
How we cite our quotes:
"I'm not trying to be a hero, but seriously, Sirius Black can't be worse than Voldemort, can he?"
Mr. Weasley flinched at the sound of the name but overlooked it. (5.35-6)
The recurring fear most people express upon hearing Voldemort's name really indicates just how terrifying Dark Lord was and still is to the wizarding community.
And then the thing beneath the hood, whatever it was, drew a long, slow, rattling breath, as though it were trying to suck something more than air from its surroundings. (5.166)
Dementors are freaking scary. The detail about the "breath" here hints at the idea of a "death rattle" or the type of breath a dying person might take. Dementors are frequently described as "sucking" things like happiness and hope out of their surroundings. We just like how the notions of "sucking" something reminds us of leeches or parasites. And fear itself is parasitic, in a way – it attaches itself to someone and "sucks" away all good feelings. Hence, Dementors are the personification of fear itself.
"It was horrible," said Neville, in a higher voice than usual. "Did you feel how cold it got when it came in?"
"I felt weird," said Ron, shifting his shoulders uncomfortably. "Like I'd never be cheerful again [...]" (5.193-4)
J.K. Rowling has said that Dementors kind of personify depression, which helps explain the reactions that Neville and Ron have here. Rowling describes depression as: "that absence of being able to envisage that you will ever be cheerful again. The absence of hope. That very deadened feeling, which is so very different from feeling sad" (source).