It took me years to discover this. I would always tense up waiting for my solo then have an asthma attack in the middle of it and run out of air in the middle of a solo. Over the past few years I've learned to release the tension while the guitarist does his solo or the vocalist is leading into mine.
Tension can lead to playing the same chops all the time because you aren't relaxed enough to create new ideas on the fly.
If I want to create tension in the song I play behind the beat, I don't work myself up to create it. The gigs go a lot nicer when you learn to relax.
It's not only harp players. Most of us probably played with band mates that had to drink hard liquor or light up a bowl before, during and after a gig to relieve the tension. Learning to tell your body to relax is a lot cheaper and healthier.
Mike
www.harmonicarepair.com