I'm so stressed at work. I can't work under the pressure! What should I do to be sane?

Stay active. Exercise is a great way to relieve stress. Your body releases endorphins during exercise, which can help you feel calm. If you exercise 30 - 60 minutes a day, your stress levels can improve. When stressed, take 5 slow, deep breaths with your eyes closed, then roll your shoulders forward 5 times, then back 5 times. This will slow your heart rate and release tension in your neck and shoulders.
Get help or new job. Can you relieve some of the pressure? Or move to another part of the company? Is there some reason you don't work well under pressure? Do you have a work counselor or coach? Maybe you could seek out mental health counseling. Perhaps you could identify the stressors and get rid of them in some way. If doing any or all of those things fail, you may need a new job.