In 2014, Nadal underwent stem cell treatment on his back at the end of the season to help repair cartilage after the injury had hampered his season.
Nadal lost in the Australian Open final after struggling with the back issue as he played Stanislas Wawrinka.
He was able to win the French Open for a ninth time but his year finished early when he had his appendix removed.
But in 2015, Nadal won just three tournaments as he dropped to five in the world.
He reached the quarterfinals of the Australian Open and the French Open but was dumped out of Wimbledon and the US Open in the second and third rounds respectively.
This year, Nadal has risen back to the top of the men’s game as he won the French and US Open to finish as world No 1.
In an interview with Spanish outlet El Mundo, Nadal has opened up about the anxiety which disrupted in his 2015 but revealed the feelings have now disappeared.
He said: “In 2014, I linked several injuries and health problems, all of which caused 2015 to start with doubts, and those doubts produced an anxiety that was unknown to me until then, the reality being that this internal stress lasted for six or seven months.
“I have not had them again, they have disappeared, what can they come back to? It is possible.”
He added: “No one fails if he does his best to win, he fails when he does not try hard enough to achieve his goals.
“Everything possible is done to win, but there are uncontrollable factors, that for me is not to fail, I have never let myself go in games or in training.”