If you are not your thoughts, but an observer of them: where do they come from?

Most times they are residual thoughts which keep repeating themselves. Other times they can be projected from outside. Important thing is to realise we aren't those thoughts.

It's the result of activity of your mind. They come from your memory, senses, and your emotions.

You don't die when in deep sleep.

your subconscious, which is vastly superior to any supercomputer

They pop right out of my thinking machine!