OAKMONT, Pa. -- Jason Day downplayed the cold he picked up, another in a long line of maladies and illnesses that seem to beset the No. 1-ranked golfer in the world.
But heading into the U.S. Open at Oakmont, Day admitted that his station in life at the moment is a contributing factor.
"I've never been more stressed in my life than right now,'' Day said on Tuesday at Oakmont, where the 116th U.S. Open begins Thursday. "It's just because being No. 1 in the world, having a lot of expectations on you, having to practice so hard to keep that No. 1 spot, trying to win as many tournaments as I can, puts a lot of stress and pressure on your shoulders.
"Sometimes your immune system gets a little heated, and you're more susceptible to getting some illnesses that way. It doesn't help that my father-in-law was sick during the Memorial (Tournament), he kind of passed it along to me.
"People ask me how I feel and that's just me being honest. I'm not trying to make excuses this week. Usually I tell people how I prepare. Unfortunately, I didn't get to prepare Saturday, Sunday. But I feel rested, which is a good thing for this week with how tough this golf course is going to be.''
Day has won seven of his past 18 worldwide starts, including the PGA Championship last year as well as last month's Players Championship. He also won the WGC-Dell Match Play Championship in March despite suffering from severe lower back issues.
He also has an excellent U.S. Open record, with four top-10 finishes in five starts, including three top-4s. Last year he shared the 54-hole lead with Dustin Johnson and Jordan Spieth despite suffering from vertigo. Day shot a final-round 74 to tie for ninth.
"The Saturday was obviously worse than the Sunday (at the 2015 U.S. Open), but obviously, there were a few spots out there where I thought I was going to quit, I'm just done with it because I can't handle it anymore, because I felt like I was going to throw up and I just felt ill,'' he said.
"To be able to know that I can push myself a little further than you think, just trying to get that next step -- mentally, more so mentally than physically. Obviously, I was kind of struggling there. But it's more of a mental barrier that you've got to break through when you have certain things like that go on. You've just got to keep pushing, keep pushing.
"Funny enough, I end up shooting 68 on Saturday and kind of folding myself into a (tie for the) lead for the last day. It didn't work out my way on the last day, kind of pushed it a little bit too much. But, yeah, it was great. It was a good experience for me to really understand how far I can push myself.''
Day tees off on Thursday afternoon at 2:20 p.m. ET with Adam Scott and Louis Oosthuizen.