She went on record saying, the dementors are a metaphor for depression and the descriptions are so scarily accurate. But sometimes other quotes work too
  1. The struggle to describe what is happening
    "It’s so difficult to describe depression to someone who’s never been there, because it’s not sadness. I know sadness. Sadness is to cry and to feel. But it’s that cold absence of felling — that really hollowed-out feeling.”
  2. Depression is a creep
    "Dementors are among the foulest creatures that walk this earth. They infest the darkest, filthiest places, they glory in decay and despair, they drain peace, hope, and happiness out of the air around them. Get too near a Dementor and every good feeling, every happy memory will be sucked out of you. If it can, the Dementor will feed on you long enough to reduce you to something like itself — soul-less and evil. You’ll be left with nothing but the worst experiences of your life." (Lupin)
  3. The feeling when depression gets ahold of you. You can see it coming, but you are helpless
    "An intense cold swept over them all. Harry felt his own breath catch in his chest. The cold went deeper than his skin. It was inside his chest, it was inside his very heart. . . .He couldn’t see. He was drowning in cold. He was being dragged downward, the roaring growing louder . . ."
  4. How depression brings back and amplifies all the worst memories- but with a strange distance- like it might not be your own or you don't recognize it as your own memory. Like Harry hearing his Mum pleading for her and Harry's life.
    "...And then, from far away, he heard screaming, terrible, terrified, pleading screams. He wanted to help whoever it was, he tried to move his arms, but couldn’t . . . a thick white fog was swirling around him, inside him..."
  5. That almost exhilarating feeling when you realize you can feel anything again- even pain. It means you are human again.
    "This pain is part of being human . . . the fact that you can feel pain like this is your greatest strength." (Dumbledore)
  6. Every time we wished we had a broken leg instead of a broken brain (this was obviously not about depression, but it works)
    "Of course it is happening inside your head, Harry, but why on earth should that mean that it is not real?" (Dumbledore)
  7. Running from it never works
    "Numbing the pain for a while will make it worse when you finally feel it" (Dumbledore)
  8. Never give up
    "It is important to fight and fight again, and keep fighting, for only then can evil be kept at bay though never quite eradicated." (Dumbledore)
  9. How depression makes you feel alone and gets worse, when you believe it
    "Well if I were You-Know-Who, I'd want you to feel cut off from everyone else. Because if it's just you alone you're not as much of a threat" (Luna)
  10. "Happiness can be found, even in the darkest of times, if one only remembers to turn on the light."
    Dumbledore knows what's up