I know many people, including myself, who've failed to succeed on 50 mpw. Many attempts end in stress fractures, Achilles problems, and other injuries, but the ones that don't feel downright miserable. You know you need to eat more, but you have no appetite, and even junk food doesn't look appealing. You know you need to sleep and recover, but it's almost as if you're too exhausted and nervous to sleep.
It's like you're on a Himalayan climbing expedition or something. Every run feels like you're dragging a load of elephants even though you haven't gone anaerobic in months. Downhill runs feel like flat surfaces, flat runs feel like climbs, and shallow climbs feel like you need hiking poles to ascend them.
And then come the races or time trials. So far, you've avoided bringing your watch or running with anyone else because finding out how slow you are would be too demoralizing. But you can't avoid the clock forever. So you take one off day, one short easy day, and then step up to the line. You're way off from your PRs, get outkicked by people you know you should easily beat, and are left wondering the following:
Why should I even go through all that if it just makes me slower?
It doesn't work like that, just because you're not hungry doesn't mean you don't need the calories. Suck it up and eat.
Also you should take your watch with you every training from now on, you're probably running the majority of your miles too fast.
Slowly starving yourself and running the majority of your miles too fast are great ways to make yourself feel like crap after a few weeks.
If those things don't help you should probably consult a doctor because you're probably not as healthy as you think you are. Stress fractures aren't normal.