I think 95% of all couples who go through this process experience stress in their relationship in one way or another. And I think that stress experienced is equally legitimate and valid for all.
Personally, in paper, our case seems like cool summer breeze (we're both together). But just two months in (plus the time preparing the application) we've experienced a lot of stress because we have invested much of our future in this process and have circumstances that make it a process with much more unknown, than known. When something is not going our way, we second guess ourselves because we've taken such a big gamble in this process.
Undoubtedly, the circumstances in some cases are truly heartbreaking and testing. I am in awe about many of the people I've read about here... many years apart, away from their children, facing rejection. It humbles my stress, but it doesn't diminish it.