A colleague of mine told me this story. When she was in grad school, another friend of hers went to give her defense. She knew her stuff inside and out, but was *really* nervous about doing the actual defense. Totally freaking out, not good at speaking in public, convinced she'll throw up in the middle of her talk. Mind you, this was in the days of slide carousels and paper notes. So she walks into the meeting room with this arm-load of stuff. And trips over the power cord to the slide projector. Note cards, references, an hour's worth of slides... everywhere.
She stood up, took a breath, and delivered a flawless off-the-cuff chalk talk on her research and was otherwise generally brilliant about her defense. She was so shaken up by falling and losing all her stuff that she basically forgot to be nervous about giving the talk and just poured out everything she knew on her subject.
Not that I'm advocating engineering a disaster to befall you immediately before your defense, but... You know you know your stuff. Better than anyone else in the room. They'll ask oddball questions to trip you up, but if you recognize those questions for what they are and deal with them as a test of your composure rather than a test of your knowledge, you'll be fine!