SAN DIEGO — Jason Day was asked Friday at Torrey Pines to describe the past three years of his life professionally. You know, sum up in a sentence or two the absence of victories on the PGA Tour, the chronic back pain stretching into a second decade and the thoughts creeping into your head that your best golf may be behind you. Describe that. “A big ball of stress,” said Day, the former world No. 1 and two-time Farmers Insurance Open champion (2015, 2018). “It’s just that you come from being the top of the world and then all of a sudden it kind of falls out beneath you. “I’m just happy that — …