The Nets flew all the way over the North Pole, halfway around the world and finally back home on Sunday.

And with Brooklyn having put its controversial China trip behind it, now comes the hard part — doing the same with the lingering aftereffects. Jet lag. Fatigue. And the invariable slow start.

“The biggest challenge is obviously the travel portion of it. There’s not a lot you can do to get around it,” Joe Harris told The Post. “No matter how you travel, it’s still a 15-hour flight and it’s still a 12-hour time difference. You try and sleep as much as you can on the plane, hydrate as much as possible, try and get your body to adapt as quick as it can.

“But you’re still going to need a couple days to get acclimated. The biggest thing is going to be [coming] back, trying to get the right amount of recovery and the right amount of rest. That way guys are feeling back to normal by the time the regular season rolls around.”

After having traveled to China last month with Team USA for the FIBA World Cup, Harris made the 15-hour flight back to Shanghai and Shenzhen last week as the Nets swept the Lakers in a pair of scrutinized preseason games. He knows full well how hard getting back to normal will be.

The NBA teams that have trekked to China during the preseason have historically suffered hangovers that lasted well into the regular season. In the Nets’ case, that means trying to shake off any malaise before the Oct. 23 opener versus Minnesota.

Over the past four years, the teams that made the China trek played to just a 41-39 record through their first 10 games before going 338-238 the rest of the way — or a 42-win pace compared to a 48-win clip.

That kind of gap — think last season’s Nets compared to the Spurs or Celtics — can mean the difference between making and missing the playoffs.

“Yeah, it’s definitely something we need to be well aware of and well-versed in,” said GM Sean Marks, who had sports science experts drill the Nets on sleep deprivation, hydration and nutrition. “I was fortunate that I’ve been on several teams that have done these trips before, and yes, you start off slow sometimes, definitely.

“But at the end of the day, it’s: What else are you getting out of these trips? You’re spreading the brand, spreading NBA basketball. It’s an incredible opportunity for our players to bond. They’re going to a foreign county where they’re going to be forced to sit down, break bread together … [have] life-changing experiences together.

“These are the things that are going to be just as important as winning a game in October or November.”

Maybe, but it’ll also be important to cash in on the soft early schedule and not waste a golden opportunity. Once the Nets try to close an unbeaten preseason Oct. 18 versus Toronto, they’ll play four of their first five regular-season games at home, three against teams with losing records last season.

It’s imperative the Nets get off to a decent start in their first seven games — just two against winning clubs — before tipping off a five-city Western swing Nov. 8 in Portland.

“The travel definitely poses challenges,” Harris told The Post. “When we were coming back from USA Basketball, they’d talked about how it was going to take a week or so to really recover. We have basically from the 13th until the 23rd, obviously we have another preseason game … but the top priority is getting ready for regular season.

“We have a good amount of time. … We’re going to have a couple off-days. Then it’s about making sure guys are taking care of themselves, getting the right amount of sleep, eating correctly and hydration is of the utmost importance.”

History shows just how important.