Dämmerschlaf
There’s a point each night between being awake and being asleep — those few moments where your brain goes completely nonlinear, but you’re still conscious enough to realize that your thoughts are getting strange. Sometimes with me it gets so extreme that I’m pretty sure I’m having thoughts that are not my own, which is a little creepy.
The other night, I was in this state for about two and a half hours before I finally fell asleep. It wasn’t restful in any way, but it was pretty interesting, especially as I generally remember most of the thoughts I have during these weird, creepy twilight periods. And I almost always use those thoughts in stories.
The older I get, the more I realize that’s where most of my good ideas come from. Most of my stories, plots, characters, and the like come to me while I’m trying to fall asleep, and falling asleep has been inexplicably rough for me these last two weeks. That means I’m full of great story ideas lately.
And I’m so tired. So very tired.
What about you, folks? When do most of your ideas hit you?
47 Echo 
For me, ideas come while walking at night, or while driving. I tend to work existing things out before falling asleep, but I don’t get too many ideas at that point. It’s usually when I’m just knocking around and something clicks and my mind thinks, “How could that have been different?” and it all builds.
Also, while reading. Not so much a thing of, “Hey, I will swipe this or expand on it,” but more like a character wanders into an attic to get something, and I think of being a little kid and how I didn’t like attics. Then imagining what I would have done had I seen a golden light spilling through the cracks of the door to the attic…and then what would CAUSE the light to shine.
I do get ideas occasionally this way. Usually the solve some plot problem I’ve been gnawing on. A couple of times I’ve woken up in the morning with solutions as well.
Most of my story ideas are merely accumulations of different ideas, ideas that were never sufficient in themselves but when paired with other ideas suggest whole stories. I rarely get a whole story idea come to me at once.
I sometimes get the main idea all at once, but rarely do I know from beginning to end where the story is going to take me. Still, sometimes huge plot points, an ending, a new character — all of that can pop up while I’m trying to sleep.