Sometimes high, when they are doing stressful things. But usually not too high - people become astronauts because they are the kind of people that can handle difficult situations without getting stressed out.
Some of the high profile things that they do would be stressful for anyone: EVAs, vehicle dockings, free flyer captures with the robotic arm, etc. (for these it would be a big deal if they messed up).
They don't do the job because everything is easy; they do it because it's fulfilling to do a difficult job well and because in doing so they can contribute to their country and to their world.
