I used to have the same problem. Mine was a symptom of my stutter I think though. I would see a short attack coming up and my throat would lock-up. It happened more often at the beginning of a piece for me than anything else. I fixed it by taking the stress out of the attack. What I mean is that I would take the first note of the phrase and just play it like a long tone until my throat eased up and then I would continue with the phrase. Then I would slowly play that first note shorter and shorter until I got it back to the way it was written. By that time the attack no longer gave me problems. After doing this for awhile with any trouble spots the problem went away.
Not sure if this is the proper method for fixing this problem, but it worked for me. I'm sure other people will chime in as well.
Hope it helps.
