Tell them straight up. I regret not doing this when I was younger because no one wants to employ anyone that comes across as a mess. And I came across as a mess. Some thought I was mentally disabled. If however, they know before the interview, it will calm you, they know what to expect, they might be able to offer you a position that will suit your needs. Please, just tell them. Unless they are arseholes, it will only hold you in good stead and they'll appreciate your honesty. Edit. I misread your post. Most still holds true though.