The 38-year-old Englishman topped the rankings in August 2012 but missed out on the 2014 European Ryder Cup team amid a downward slide which coincided with a change of coach.
"My confidence had taken a big knock and I asked myself if I wanted to continue doing this," Donald, who last won on a major tour in 2012, told the Sunday Telegraph.
"I wasn't enjoying it, finding it so very hard and could not see much light at the end of the tunnel. But then I told myself not to be a baby, to grow up and realise how lucky I was. I was still playing golf for a living."
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In his pomp, the four-times Ryder Cup winner was known for his almost laser-guided iron play and a superb short game, but after an unsuccesful year-long stint with coach Chuck Cook, he rekindled his relationship with long-time mentor Pat Goss in late 2014.
Donald also sought the help of sports psychologist Michael Gervais, who helped Austrian skydiver Felix Baumgartner become the first human to break the sound barrier without mechanical help when he plunged from a helium balloon 24 miles (38.62 km) up in the stratosphere.
"He just reminded me that it's up to me what mood or mindset I'm in," added Donald, who was "sacked" by long-time caddie John McLaren in October.
"When you're in a slump it's easy to forget you're still the one who is in control."
Donald, who has won more than 35 million pounds ($50.81 million) in his career, is now ranked at 78th in the world and needs to get back into the top 50 or win on the PGA Tour to qualify for a 12th consecutive U.S. Masters at Augusta in April.
"I think I have a little way to go, but I'm feeling confident that I can get back to at least close to a level I was a few years ago," he added.
(Reporting by Rob Hodgetts, editing by Pritha Sarkar)
