This is an excerpt from Elder Robert D. Hales book Return: Four Phases of Our Mortal Journey Home.
When I was a young General Authority, I had the opportunity to accompany President Spencer W. Kimball to many area conferences. During the planning and preparation for the Mexico and Central and South America area conferences in February 1977, we were scheduled to hold meetings in La Paz, Bolivia, which is twelve thousand feet above sea level. President Kimball should have four to six hours' rest to acclimate his heart and blood pressure to the high altitude. President Kimball was very tightly scheduled during area conferences, and this allowed him little time for rest. (in reality, the doctors accompanied the General Authorities so that we could keep up with President Kimball!)
I talked with President N. Eldon Tanner and President Marion G. Romney, President Kimball's counselors, to seek their assistance in getting President Kimball to rest in La Paz before the start of the area conference. They only smiled and said, "You can try."
Detailed plans were presented to the First Presidency for these area conferences. I saw President Kimball make two small red check marks next to La Paz, Bolivia, where there were two meetings that he was not scheduled to attend. "What are these meetings? Why am I not attending?" he asked.
There was a pause, and then I replied, "That's a rest period, President Kimball."
"Are you tired, Elder Hales?" he asked.
Return: Four Phases of Our Mortal Journey Home. Pg 177