I am always so sad when I hear of someone with ADD feel that their hard earned success isn't deserved. Your work can't be all that terrible if you're successful, but I can understand wanting the craziness to stop try a coach. There are ppl out there that coach ppl with ADD/ADHD. They can teach you skills on organizing stuff so it works for you, how to break projects down so you can work on them a little at a time, and not have to rush around pulling things together at the last minute.
I used to feel like a fraud at work. Everyone else seemed to be more organized, focused, and just plain pulled together than I was. Then I started thinking, with as prevailant as ADD/ADHD is, how many of my coworkers feel the same way? How many others struggle like I do to "keep up" appearances?
Have you considered trying another line of work? One that will allow you to not feel so down on yourself, but would still allow you to use your existing skills? Have you tried meds? I do also find that my feelings of "lunacy" as you put it have lessened since I started talking to others with ADD. Holding it in and trying to hide it makes it worse, because its all just sitting around frementing in your head.
I am 29 and very succeful for my age. Mostly, I feel like I get away with murder because my work is terrible, I am unorganized, etc. I am only able to fool people because I am smart and I can pull things together at the last minute. My car is a mess inside, I have always been called lazy or compulsive when I find something that finally interests me. I want to change and I will sacrifice some of the lunacy and creativity for focus and structure.