I also have never disclosed until I was hired.
I'm fortunate to work where I do...everyone is amazingly understanding and comprehends the disease. My secretary now has the ability of looking at me and she can discern whether I'm starting to fall. It's nice to know that there are some work environments that aren't totally hostile (previously, I had worked for a few firms like that, where keeping it a secret was the thing to do because the culture just wasn't open to anyone having any perceived 'issues.') I once had an HR person ask me after I had had a low spell and had been falling out at my desk whether I could do that someplace else, because it 'sends a bad message.' Like if I could control that at that moment I would totally be losing consciousness at my desk. Idiot.