"Lying down" means resting or reclining with your body flat on a bed, couch, or floor.
People lie down to rest, sleep, ease pain, or recover from illness or fatigue.
In phrases like "take it lying down," it means accepting something without a fight.
A dog teaches a boy fidelity, perseverance, and to turn around three times before lying down. Robert Benchley
A boy can learn a lot from a dog: obedience, loyalty, and the importance of turning around three times before lying down. Robert Benchley
I have remarked very clearly that I am often of one opinion when I am lying down and of another when I am standing up... Georg Christoph Lichtenberg
Look, here are we on this starry night staring into space, and I must say I feel as small as dust lying down here. Dave Matthews
On the plus side, death is one of the few things that can be done as easily lying down . Woody Allen
Never do anything standing that you can do sitting, or anything sitting that you can do lying down. Chinese Proverb