The 28-year-old from Bristol rose to a career-best 46 in the world rankings as a result of his nine-under-par finish.
"It's hard to believe because I was on a drip for 13 hours," Wood said.
"The heat got to me and there was no chance of me playing the way I felt, so to finish fourth is a massive result."
Wood, who ended the event in Sun City four shots behind runner-up Henrik Stenson and 10 strokes adrift of winner Marc Leishman, says even making the first tee on the opening day was an achievement.
"I was wheeled through the hotel in a wheelchair and tucked into bed by two doctors and I was in a bad way - so, whatever the result was this week, I was glad to be playing," Wood added.
"I've enjoyed my whole week here and it gives me a good step going into 2016 - especially in Ryder Cup year."
Englishman Chris Wood says his third-place finish at the Nedbank Challenge in South Africa was "massive" after revealing he had been in hospital on a drip on the eve of the tournament.