Pre-date nervousness is natural and, if managed correctly, can even be endearing. There's bound to be awkward moments, butterflies, and sweaty palms. It's ok. If you don't allow the jitters to be overwhelming they can show your date that you are vulnerable. Vulnerability = attractiveness, especially if you are a man. Chicks dig vulnerable guys.
What is not ok is telling your date that you are intimidated by them. If you are out with someone that intimidates you it's time to do a check-in;
Do you think your date is out of your league? Then thank your lucky stars they asked you out/agreed to go out with you! And for crying out loud, don't admit it! That's just saying "I really don't have a whit of self-confidence". Sexy.
Are they doing something that makes you uncomfortable? Its probably time to cut things short and move on to greener pastures. Life is too short to voluntarily be around people that are weird or judgemental or smell bad. Go home, open your favorite beverage, turn on some Sinatra and give yourself a pedicure, even if you are a man. Nice toes are sexy.
Update: My mother is home from the hospital and doing ok. She left with a lot of hardware, 4 cardiac stents, and will have one more placed in a few weeks. I dealt with my mini-breakdown by taking a deep breath and reminding myself that no one was actually dead yet.