I am a long term smoker, is it true that i will get sick if i suddenly quit ?

Quitting is GOOD: No! you will have to deal with controlling the oroblem of addition and often until your respiratory musosa settles down you may be more sensitive to other smells or irritants. There are treatments available to assist with the addition component. The immediate and especially long term health benefits greatly outway any short term negatives. You can do it!

Quitting smoking.: Cold turkey is the best way, but nicotine or cigarette tapering are viable options as well. For cold turkey, pick a quit day in advance, prepare for it, and go for it. You'd feel less sick with one of the tapering methods, but cold turkey is more successful in the long run.