Yes, yes and yes.
The fog is the fog. Which is why they call it that. LOL
It happens to me at work all the time. I do make mistakes but the great thing about mistakes is they can be fixed. As long as you can fix what you have done, then they should have no issue.
As for telling, I would go with a case by case basis. If its the meds, talk to your docs about it. If its the FM, decided whether or not you want to tell people you have FM.
FM should not be a stigma but it is.
Remember FM affects the brain as well as the rest of the body.