@farshad, were you taking regular niacin? There's several kinds for sale, I think it's the regular niacin that you have to try out. (see my new edit, I realized I might have said something I'm not sure of so I deleted it).
You definitely should go lower, and on real niacin, not the treated kind. Like I said, I took 50, maybe one of these days I'll try more, but I'm not having the spacey symptoms as bad so maybe not.
I'm not sure how much, it's probably individual, but I wouldn't ramp it up that fast, but that's just me. Maybe someone will comment that knows more. Good luck.
Edit: I've read taking it at night keeps the down in the dumps feeling away, but you're trying to fix what? Overmethylation? Because if you under methylate (I think this is right) you may be taking it too far. I think it's the over methylators that can take a lot.