I apologize if I have misunderstood what you said, but I want to give it a go 'cause I know this must be causing you a lot of pain.
Something that doesn't exist can't examine itself and ask if the thing it calls "itself" is real. If something isn't real it can't ask if it is real because there is nothing to ask that question. Does that make sense sort of? I think therefor I am. So you must be real.
As for other people and wondering if you are in a coma or something similar I'm less sure about, not that I think that is the case, just that I'm not sure how to go about proving that everyone is real and such. Perhaps learning new thing's could be a reason to think that the world exists outside your imagination; if the world was created by your mind maybe you would then feel like there wasn't anything you didn't know. If I write a story I will know exactly what happens in it because I created it. If I read a book and don't know what will happen in it then that should mean that it isn't a creation of mine. So, if there are things that you have to learn about by experience or from other people and you feel like you actually had to learn it and it's not something you knew all along, that should mean that you didn't make it up.
On another note, your entire life and everyone and everything in it is very complicated and big. It's a lot to make up in your head, you know?
I hope someone with more experience with feeling like you do can answer you and help. I'm sure there are people out there who feel exactly the same. Hopefully at least a little bit of what I said is helpful.