Are you in a habit of doing things at the last moment??Are you in a habit of procrastinating things.??What is happening with you is very common .Dont worry.A little stress n axiery at the time of interview is good.
Now as you said earlier it was not happening to you.you didnt get stress n you used to take things easily.
Now its happening may have many reasons..May be you taking yourself seriously now. One more thing may be you looking for the perfection and you are not able to do what you are expecting from youself.Solution is simple give more time in preparing yourself.
Next Steps
Well ptepare yourself for any interview or group discussion before hand.Feel confident .
Health Tips
Give mock interview..Stand in front of the mirror and start preparing yourself for the interview. Its going to help you.Will boost your confidence. Say it to yourself i m prepared n i m confident .let me know if it helps you.Tc .