Paris - I was almost down and out before Roland Garros triumph - Nadal
"I was not enjoying it too much, I was worried about my health. I was down mentally and physically after Indian Wells," said Nadal.
"I was too negative. After Madrid and Barcelona, I was thinking about what I needed to do. I could stop for a while and recover or change my attitude and recover."
After a loss in the Australian Open final to Novak Djokovic, where he won just eight games, a second round exit in Acapulco was followed by a withdrawal from the semi-finals in Indian Wells, when a knee injury meant that an eagerly-awaited clash with Federer was shelved.
His return in the clay court season saw semi-finals losses in Monte Carlo, Barcelona and Madrid before a much needed title triumph in Rome.
"In 2018, I played nine events and finished just seven of them," Nadal added.
"I had issues with my knee and surgery on my foot, so many issues in the last 18 months that have made the last few weeks very special."
Nadal revealed that in Barcelona, he had even locked himself away, questioning where his season was heading.
"Mentally, I lost a little bit of energy, because I had too many issues in a row. It is tough when you receive one after another, and then sometimes you are groggy," he explained.
"In Barcelona, I was able to stay alone for a couple of hours in the room and think about what's going on, what I need to do.
"One possibility was to stop for a while and recover my body. And the other was change drastically my attitude and my mentality to play the next couple of weeks.
"Thinking a lot, finally I think I was able to change and was able to fight back for every small improvement."
On Sunday, Nadal took his Roland Garros record to an astonishing 93 wins and just two losses having previously won the title in 2005-2008, 2010-2014, 2017 and 2018.
It also gave him an 82nd career title and 950th match win.
"All the things that I went through probably give me that extra passion when I am playing, because I know I will not be here forever.
"So I just try to be positive, to be intense, and to be passionate about what I am doing."
Next up for Nadal is his latest assault on Wimbledon, where he has twice been champion, in 2008 and 2010.
However, the All England Club has also been the site of some spectacular lows.
He lost four years in succession to players outside the top 100 - Lukas Rosol, Steve Darcis, Nick Kyrgios and Dustin Brown - from 2012-2015.
In 2017, he was knocked out in the last 16 by Gilles Muller, 15-13 in the final set.
Last year, he lost a marathon semi-final to Novak Djokovic by dropping the last set 10-8.
"I played a great event last year. I have been able to be very close to win another title there. As everybody knows, I love to play on grass," said Nadal who added he will not play a warm-up event before Wimbledon.