Interview is the stage of the recruitment process where candidate's faith is being determined and in most cases after performing very well in the aptitude test, some people can't prove that they are not theorist.
     This may be a lost opportuinty of a life time which may never come around again, i guess the major reasons  for shivering in an interview panel are;

1. Fear of missing the questions that may be asked.
2. lack of confidence in oneself
3. inadequate preparation
4. shyness i.e fear of facing panelists
5. others
         
          Suggestions for overcoming these problems ;
1. Aduquate preparation for the interview
2. Attending a relevant seminar on this issue
3. apply to some small organisations to aquire experiences and prepare you for big ones
4. PRAYERS.

        I welcome more reasons for poor performance in interview and at the same time solutions therefrom

and seeing it as not a 'do' or 'di'e affair. if u get it fine. if u dont, life continues. Again, to build some confidence, you need to dress well and look well, when u are shabbily dressed, when u see other applicants invited u started feeling inferior, and thats when nervousness and anxiety set in.