Where do New Ideas Come From?

As I think about all the ideas that just suddenly come to my mind, it makes me wonder, 'Where DO these ideas come from'. Sometimes, I think that they just suddenly appear, out of random and for no reason whatsoever. Other times, I think that you get ideas from seeing things. For example, by reading a book, you get an idea on how to start your story or how the plot goes. Now that I thoroughly think it through, I believe that we get ideas from both seeing things and our brain's creativity. Some of you might disagree, because your not a person who has to see something to remember it. Maybe you hear some one's idea but change it so that's its new and is yours. That is very possible too. Also, for me, I am only able to think of new ideas when I'm in a quiet area with a calm state. It is not possible for me to think of many ideas when I'm stuck in chaos. The easiest time of day for me to get new ideas is at night. I'm not sure why this is, but when I'm just about to sleep, tons and tons of new ideas start flooding into my brain, so much so that I am not able to sleep. This is my personal opinion, but 'What about you? When do you get fresh new ideas? Where do you think they come from?'