Monday at a non-major golf tournament is usually pretty sleepy. Players trickle onto the grounds, check in, get the lay of the land, maybe hit a few balls or roll a few putts. Many of them don’t even turn up at the course until Tuesday for a practice round.

Gary Woodland wasn’t just at Jersey City’s Liberty National Golf Club on Monday in advance of this week’s Northern Trust, the first of three FedEx Cup Playoff events. He was grinding.

Woodland, the reigning U.S. Open champion, spent five hours on the practice range with his swing coach, Pete Cowan, trying to regain the form that helped him win his first career major championship in June at Pebble Beach.

Since that win, Woodland has played three tournaments — missing the cut at the Rocket Mortgage Classic two weeks after the U.S. Open, missing the cut at the British Open two weeks ago and tying for 55th last week at the Wyndham Championship.

That’s why he was on the range on Monday and back on Tuesday for about an hour before playing a practice round.

“I just needed to reset,’’ Woodland told The Post on Tuesday between range time and his practice round. “I had a little bit of fun that week after [the U.S. Open] and just showed up [at the Rocket Mortgage] and wasn’t ready to play, and I kind of got into some bad habits, and it’s leaked on for the last month.

“[Tuesday] was as good as I’ve swung it since the U.S. Open. It was nice to get back to work. These are three big weeks with a lot at stake.’’

There’s more at stake for Woodland than simply the $15 million first-prize payout at the end of these playoffs. Woodland’s goal is not to become a one-hit wonder, not to let that U.S. Open be the only major championship he wins in his career.

“The goal for me now,’’ Woodland said, “is to win the second one.’’

Since his U.S. Open win, Woodland was celebrated by his hometown of Topeka, Kan. And his wife, Gabby, gave birth to identical twin girls, Maddox and Lennox, last week.

“It’s been a whirlwind,’’ Woodland said. “But it’s been tough, because my wife’s been in and out of the hospital for the last month. So it’s been hard to enjoy it too much. Last week was a huge relief, with the girls coming on Thursday.’’

Keegan Bradley recalled the blur life became after he won his first — and only — major, the 2011 PGA Championship.

“It was my rookie year on Tour so everything was pretty crazy, and then I won the PGA,’’ Bradley told The Post on Tuesday. “I threw out the first pitch at Fenway, I dropped the puck at a Bruins game, I flipped the coin at a Patriots preseason game. I got a text from Tom Brady. Bill Belichick sent me bottles of champagne. These are like childhood heroes of mine. It was crazy.’’

Not surprisingly, Bradley missed the cut at both FedEx Cup events, in New York and Boston, that followed the PGA he had won.

“You’re so tired,’’ he said. “Everything was so fun and exciting, and it’s hard to come down from that.’’

That 2011 PGA was the first major championship Bradley ever played in. He hasn’t won a major since, a pitfall Woodland is trying to avoid.

“After you win one, you want that feeling again,’’ Bradley said. “It’s almost like a drug. The feeling is so amazing. You crave that again. The respect that you get out here when you win a major is so different than when you win a regular Tour event. When I look at guys that have won major championships, I look at them differently.’’

Jim Furyk, who won the 2003 U.S. Open and hasn’t won another major despite numerous close calls, compared the questions from people about winning a second major as “kind of like having kids.’’

“When you don’t have any kids, everyone asks you, ‘When are you going to have kids?’ ’’ Furyk said Tuesday. “Then, when you finally have a kid, they ask you, ‘When are going to have your second?’ ’’

Furyk remembered the “whirlwind’’ effect he felt after winning his U.S. Open.

“I played Westchester the next week and I made a lot of dumb mistakes, put a lot of pressure on myself, tried too hard,’’ he said. “It’s tough to come back after a major. You have a little bit of an emotional hangover.’’

This is what Woodland has faced in the past month and a half. It’s what he faces this week and what he’ll face until he regains his form, until he wins again, wins another major.