They don't sound good do they? (Makes you wonder a) where this stuff (side effect information) comes from or b) if they add something else to niaspan (Johnwen?) I guess I'll check wikipedia. In any event, odds are excellent you won't experience any of these, and they are not life threatening, compare and contrast to the real side effects of crestor! (At least "major organ threatening" and statins have increased the incidence of heart transplant by a factor of 3 since their inception.)
Here is an good wikipedia article on niaspan http://en.wikipedia.org/wiki/Niaspan
Note a more reasonable set of side effects, although I don't trust the multi-gram danger knowing the work of Hoffer and Pauling. (Someone somewhere is able to insert these supposed dangers of "mega" vitamins.)