I suppose a lot of people do this...
I find that the time when I get ideas, are when I am just going to sleep or just waking up. I often used to repeat things over in my head so that I would remember them the next day, but that definitely didn't work. So what I do now is always have a pen and paper beside the bed so that I can write it down, in the dark, and let my mind rest at ease that the idea will be put into action in the near future.
Except sometimes I wake up to find notes like this one.
I can make out -cute girl cards...okay, - paint (some kind of ) dog...okay, if otters were people..huh?, and aliens (doing something ) to my head...double huh?