When you’re lying in bed, or driving in the car, or you’re somewhere where you can’t write things down and you come up with a great part of your story. It just flows so beautifully and is a scathingly brilliant addition.
Then the next morning, when you settle down at the computer, open the document up and are all ready to go the idea is gone. You have absolutely no idea where you were even going with the idea. You sit there and rack your brain to get just a sliver of that idea that had been so wonderful, so inspiring.
I really need to keep a notebook by my bed so when this happens I can write it down because that happened last night and I have absolutely no idea what I’d come up with.
Maybe it wasn’t so brilliant after all.
Cerian Hebert 
I usually get up and write it down — or else I boil it down to one sentence and repeat it over and over and over until I have it memorized… most recently? “She is trained by her sister.”I know, doesn’t sound earth shattering, but it really is… lol
I hate that when it happens. I think of something great before I go to sleep and think I won’t forget it but I do. I have done what Marianne does and keep repeating it to myself before going to sleep. But the best way for me is to just get up and hurry jot my ideas down.
Or one of those voice recorders. I have one for my car. . .but I have yet to actually use it.
I have one of those recorders too. I bought it with the intention of using it when I went for walks because I always got good ideas when I walk. But I felt foolish using it. I don’t think it works anymore.