I used to get pretty bad, finally subsided my second year when we had practicals about ever two weeks. I learned a little control and just got used to the "pressure cooker." I did consider prescription meds, but a combination of not personally approving of their use and worries of them negatively affecting my performance (was too affraid of being too laxed) kept me away.
This is what worked for me, your school may not allow you to do all of these things
1. What's the big rush? I started all my practicals late, up to 15 minutes late. As soon as the instructor said go the whole place ignited with high speeds and a no talking for 3 hours. Not the most chill of atmospheres. I sometimes didn't even fully set up intentionally so that I took 5 minutes to get my stuff together while all others blitzed away. Just take some time to get relaxed and out of the confusion fueled by your classmates.
2. Block it out We could use headphones, but couldn't talk. If you can do this do yourself a favor and buy some nice noise cancellation headphones plug em into the Ipod, turn on a relaxing playlist. If you can't use headphones just stick in some earplugs, they are like $0.15 at Wal-Mart. With no talking all you could ever here were three things in the background; 1.Highspeeds 2. "YESSSSS" and 3. "F#$K!!!!!!!!!!!" Don't let that get to you. A couple practicals I just sat and listened to music for a song or two with my feet up on my lab bench for those first few minutes to relax as well. I know, I know, not all that professional, but it worked!
3. Take an F'in break. At a good halfway point? Go out in the hall, get a drink, say hi to the people hanging out in the building, go for a walk outside,watch 3 minutes of Sportscenter on the TV. This really helped break it up, ESPECIALLY if you are in a jam. If you find yourself in a sudden panic remove yourself from the situation. Take a breather and come back and asses the situation with fresh eyes. This is where I used to go Ape S&$T. When I thought I made a mistake I instantly started shaking. I had a buddy who would just go intol panic attacks, this worked for him as well. Just leave and clear your head. The last thing you want to do is start fixing things while you are distraught.
4. Don't pay attention to anyone else...EVER Comparing yourself by monitoring Sally Sue next to you who whips out perfect crown preps in 8 minutes is going to land you in nothing but a panic. Just focus on your work. Just because others have finished doesn't mean you need to hurry. Who cares if you miss out on lunch with your friends because you took an extra 20 minutes to tweak some things? Do YOUR thing
5. Practice makes perfect Take the time, learn what you do right, what your common mistakes are. Have someone critique your work. But, don't over-practice. Make sure you know what you are doing and how to fix any problems and get some sleep. Staying up all night is only going to start the panic train. Do a good practice round and end on a good note,that way you have nothing to worry about leading up to the real deal.
6. Know when to guit!!! One of our instructors always says "Better is the enemy of good enough." I can't think of anything better. If you know everything is fine, then check the hell out!!! Don't try to fix little things in attempt to go form a B+ to an A-. This is where I used to always get in trouble, trying to make things just a hair better. Know how to properly evaluate yourself. When you have everything good by all means don't make anything worse! I know it's hard, we are all perfectionists. Remember you can always take away ivorine, but you can't put it back.
Ok, I guess I have 6 practical commandments. I think lover's should make up the 7th but I think you can figure out that one on your own. Godspeed and just relax.