After years of mountain climbing, David Hillebrandt learnt how to deal with his altitude sickness.
"In 1980, my wife Sally and I drove to Kenya from Britain as part of a world drive. I suppose you could have described me as a tough and rugged young doctor and an experienced climber. Sally didn't climb at all.
"Before my ascent of Mount Kenya (5,199m), a technically challenging rock climb, we decided to walk the little-used but magnificent high-altitude trek around the mountain to acclimatise.
"It was quite a humbling experience for me as we progressed along the beautiful trail at between 3,000m and 4,000m. Sally was happy and healthy and enjoying the wonderful flora as we crossed amazing ridges and valleys, but she watched me being slowly overtaken by altitude sickness.
"I was soon suffering from a terrible, severe, throbbing headache worse than any hangover, and vomiting up everything I ate.
"We planned a celebration for my 27th birthday, but all I could do was be sick. Sally must have been tempted to laugh at me, a great mountaineer reduced to a liability.
"I must admit, I did slightly resent her apparent immunity to the horrors of altitude sickness. We're just genetically different."
"I went down to a lower level for some relief from my aching head and enjoyed a good meal. That did the trick, and I was eventually able to climb the magnificent mountain in two days with no trouble.
"I couldn't have completed the rock climb if I'd been feeling ill. Being careful to acclimatise properly did take extra time, but I was very glad I'd done it.
"We got up to the summit in one day and dropped down about 100m to sleep tied to a ledge. Waking up to a fantastic dawn overlooking the African plains was something I'll never forget. It was certainly worth the effort, altitude sickness and all.
"Since then, I have become older and wiser, and I have learnt to go slower. I have climbed in the Himalayas and psychologically adapted to altitude sickness, but physically things are the same.
"It's still as bad as it was 30 years ago. The only difference is that now I know how to deal with it."