It seems that there is the implication that a grading exam is a stressful situation...Why would it be, when you think about it --- particularly for kyu grades.
I've often wondered this myself. I've talked about this with people in our dojo who have to deal with real life & death stress in their daily lives. Police, emergency room doctors, emergency medical tech. etc. All of them have said that their aikido gradings have been some of their most stressful times. In talking with them, and in my own experiences it really comes down to more of a performance anxiety than any type of physical stress. All of the people I've talked with have gotten themselvs so worked up in the time prior to testing that they fill themselves with self-doubt. It's not like the stress of outside situations where you don't have time to think about what's going on. Before the test you may have days/weeks/months to think about it. Lots of time to think of all the horrible things that could happen to you during the test