As per the sources the truth behind the Rajini illness is he stooped the habit of drinking alcohol. Rajini usually takes few pegs of Whiskey everyday and he could have as many as eight to nine pegs of whisky on occasions. Rajinikanth family members and his spiritual Guru had advised the 60 year old actor to stop the drinking alcohol by considering his health conditions.
However, on his birthday (December 12, 2010) the actor decided that he would kick the drinking habit. And eventually, a couple of months ago he gave up drinking and from past two months he is not drinking the alcohol. Because of his decision to quit alcohol drinking, he gets a bit restless sometimes. So this makes him sick.
Speedy recovery and soon he is going to come back on to the sets of Rana with good health!