When interviewing you shouldn't have to tell them anything...just interview for the position. They are not allowed to ask about any disabilities and can only take that into consideration if you need accomodations that would put them under undue hardship. That said...you need to be honest. If your condition could affect attendance, number of hours you can work per shift, etc and the company will be to accomodate those things then you need to tell them that. All interviews I have ever conducted involve questions like, "Is there anything that will afftect your ability to come to work on time every day?" or "Can you lift at least 40lbs?" Etc. In those cases, you need to be honest. But there is no need to explain the details of your condition unless you are expecting them to make special accomodations. And if you will need special accomodations, you should think about what you will need beforehand so that you can have an open and honest discussion with the employer. Not sure if that helps or not.

With people I already work with and anyone else who asks, I generally answer any questions but keep it limited unless they really want to know the details. This condition is too hard to really explain to someone who is just asking a casual question.