What can I do to calm my nerves before an interview?

I am a very capable person? I am a manager where I work and I have many responsabilities. I work in retail so I deal with a large amount of people on a daily basis. I'm ready for a new career, something outside retail. I recently applied for a good job and had my interview last week. My interview was with a panal of five people, I was so nervous all I could here was my heartbeating in my ears! My answers did not reflect my capabilities AT ALL! needless to say I didn't get the job. I am not this person, I am usually calm and confident. How can I better prepare myself for my next interview? Now that this has happened I'm afraid I'll be that way next time!
Answer:    I'm a high school career counselor and all you had was a bad case of anxiousness.
A panel interview is difficult because, in your case, you were dealing with five people instead of one. But now that you have this experience the next time you interview make sure you practice your responses with a friend, family member or a mirror before the scheduled interview. While your practicing you'll want to get into the habit, and be comfortable with, making eye contact with all the people on the panel. Panel interviews are an easy way for companies to have "key" people interview you at one time but it is stressful for the interviewer. When you practice imagine yourself making eye contact with different spots on a wall ... each spot is a different person. The more you practice this technique the more comfortable you'll get.
With ample practice you're next interview will be better (and you should be more confident) and hopefully a job offer will follow.
Think something funy
Envision yourself acing the interview, know that you will wow them. And when you face another panel interview, view it almost a game of strategy. Have the attitude "I'll show you that i'm not intimidated and I will ace your questions one person at a time". And lastly don't forget to smile the whole time, and smirk if you have to! :>
Try to anticipate the questions. Now that you know what types of questions you will will get on an interview, think of responses ahead of time.
Do you have gaps in employment? Tell what you did during that time. How can your management skills transfer to a new job? What is your management style? If it different from the company you work for, tell how that could be an advantage. Basically you're selling yourself. Good luck with the next one.
This indicates that you were not the slightest bit confident about getting the job, I'm afraid. Not only that, but you felt like your world and all your future ambitions were riding on getting that job. It's not. You are going to be successful regardless of what company you work for, and dammit, if they don't hire you, it's their loss, not yours.

Next time, go in with the attitude that they are meeting their future president. You are going to kick * and take names in that company, and make that company better than anyone could possibly dream today. (An attitude, not an "attitude", know what I mean? LOL)

What's your favorite happy song? Mine is VH's "Jump". Listen to your fav happy song right before you go in for the interview.
People do feel intimidated with the things they want, in your case it's the job. From what I see, you have not used the your ability to get what you want, cause you had let your feelings to overcloud your judgements, and just to let you know, it's not your fault.
However, you could take this as a lesson learnt, and when the next time comes around, you could take this lesson as a reminder. Having a panel of 5 this time, does not mean you will have the same panel again, worst, it could be a panel of 8 or 10 in future.
So be prepared....remember to take a deep breath and to remind yourself on your achivements as well as experiences, cause you're not gonna let intimidation to win next time!
I was like this when I was interviewing the first time out of college and bombed the first few interviews. I then went into an interview where I really didn't care for the job and aced it. Got the job offer and after I heard about all the benefits I ended up working there anyways. But back to your point. After acing that interview I went into every interview with that same mentality...don't care if I get this job. It made me more calm, but you definately need to keep that mental state otherwise your nerves will take over and screw everything up.
Confidence comes with the feeling that you are going to do well. Fear is due to the feeling that your answers do not satisfy the panel of interviewee.
Have mock sessions of interview with your friends role playing the persons conducting the interview. It may help you to overcome your nervousness. Presentation skill and communication classes will be of help.