Personal Interview is a dialogue between the candidate and selection panel members who are curious and equally anxious to reaffirm on your abilities which you have exhibited in your entrance exam, WAT, Essay, Extempore Speech and in GD.
Chances are very high that not only you will be asked to relax and reply but sometimes you might face teething questions based on your academic background or based on your own responses.
Being natural in reply and be as you are will accrue right gestures and to the point answers. Both your body and mind must synchronize in natural way to react or respond to every query of selection panel. This will motivate them to feel confident for you as candidate.
With simple natural answers you will be equally gaining confidence and likely to be heard in PI.