The 35-year-old flourished over the first three rounds before closing with a seven-over-par 79 and a tie for 37th in the opening major of the year.
Singh, who shared 16th place going into the last day, never recovered after running up an ugly quadruple-bogey eight at the uphill opening hole.
"I couldn't get my focus back after that bad start," he told reporters after playing with former world number one Vijay Singh in the final round.
"I kept trying hard on every shot but I couldn't do anything. I had some bad breaks as well but that's golf.
"I'm really disappointed. I enjoyed everything this week except for the last round at the Masters.
"I'm happy that I made the cut and I would love to come back as I like the course. It's set up perfectly for my game."
Jeev Milkha Singh, who won four titles on three separate tours last year and topped the Asian order of merit in 2006, plans to play in next week's Heritage Classic on the PGA Tour before taking a break.
"I need to take some time off to sort out some things that are bothering me," he said. "My scores in the last round especially have been disappointing this year.
"I need to sort that out before I get out on the golf course. It's more a mental thing.
"I don't normally take things too hard and often take it as another round but this last round hurt me," he added.
