I actually have an interview with Google in a week or so, and I'm absolutely terrified. After some reflection, I realized that I'm not afraid of not getting the job - I like my current job and wouldn't mind staying. I'm fundamentally afraid of failure - of being unable to do well on the problems and having the interviewers think I'm stupid. It's so silly, because I'll likely never see these people again, and I should be confident enough in myself and my abilities to not let their opinions affect me at all, but there it is. What if I can't make heads or tails of the weird binary search problem they give me? What if I get confused (I ALWAYS get confused) trying to manipulate a linked list? What if I get sent home after the first one or two interviewers? What if this reflects poorly on the Googler who recommended me?
I feel like a coward for being afraid of this stuff.
I was in an identical position 3 weeks ago and I shared some of your concerns as well. I can tell you that it seems scarier than it really is once you're in it. You shouldn't be worried about getting 'stuck', I did a number of times and quite often would get hints and directions from the interviewer. Never give up, even if what you know you don't know the answer right away, let the interviewer see that you're thinking and try to engage a discussion.
And really just try to take it easy. I was also under a bit of pressure, but think of it like an experience, even if you end up not passing. It's just another company and the feedback of 5 random people.
I feel like a coward for being afraid of this stuff.
Anyways, I just wanted to get that off my chest.