Jason Day of Australia watches his tee shot on the...

Jason Day of Australia watches his tee shot on the ninth hole during the second round of The Barclays. (Aug. 27, 2010) Credit: Getty Images

PARAMUS, N.J. - This season, Jason Day has had no trouble following that old golf dictum, "Keep your head down." If he didn't, he would get sick to his stomach.

He has been playing all year, winning the Byron Nelson Championship in May, with what he had thought was a sinus problem. All he knew was that if he got up quickly or raised his head abruptly, he would become nauseated. Eight doctors haven't been sure what to make of it, but at least a couple said Day would need an operation.

Lately, for some reason, he has started to feel better. What's more, a visit to an ear-nose-throat specialist revealed he does not have to have surgery. "He goes, 'You might have mono,' '' said Day, a 22-year-old from Australia. "I tested positive two out of the four panels for mono. So I don't know that I have a minute case of mono, but we'll see."

Whether it's mononucleosis, sinus, Lyme disease or something altogether different, it hasn't stopped Day. He made three birdies in his final five holes Friday and finished a solid 4-under-par 67 to go 8 under and hold the 36-hole lead at The Barclays.

Figuring how he did it was an easy diagnosis: "I drove the ball well, and I hit my second and third shots into the greens as well. I was just trying to hit the greens, get myself opportunities."

What he will do the rest of the year is give himself an opportunity to rest "and get on top of this health thing, because I can't keep playing, the way it has been."

"I'll get really tired, real weak and shaky out on the course," he said. "When I'm at home, I just do nothing. I just sleep a lot. My wife takes care of me, which is good. I'm just really kind of excited that I'm on top of the leader board right now with really poor preparation."

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