wait, by "choke" do you mean your vocals just choke or you choke on your guitar playing? or both?
I mean, I have the vocal problem sometimes, where I get way into the song, then forget what Im singing and what comes next so I freak out for a second and screw up. I guess just thorough memorization can fix that.
if you start getting way into your vocals and are forgetting what you're playing on guitar, well...same thing applies. drill it constantly.