"Very thankful to everyone who has reached out," Efron, 32, tweeted Sunday. "I did get sick in Papua New Guinea but I bounced back quick and finished an amazing 3 weeks in P.N.G."
The star went on to share that he's home with his family and friends for the holidays.
"Thanks for all the love and concern, see you in 2020!" he concluded.
Efron was filming the new series when he apparently became sick from an infection, per The Sunday Telegraph, which reports he was flown to a private hospital in Brisbane, Australia, and underwent treatment for several days.
The "Baywatch" star reportedly flew back home to the U.S. on Christmas Eve. The newspaper reported Medical Rescue Group, a medical evacuation company based in Australia, recently flew an American in his 30s from Papua New Guinea to Brisbane.
Efron's latest project, "Killing Zac Efron," was picked up by mobile video platform Quibi, The Hollywood Reporter reported last month. The show is said to follow Efron — who became a household name after Disney's "High School Musical" movie series became a hit in 2006 — "as he heads deep into the jungle of a remote, dangerous island, falling off the grid for 21 days."
"I tend to thrive under extreme circumstances and seek out opportunities that challenge me on every level," Efron said in a statement at the time. "I am excited to explore any uncharted territory and discover what unexpected adventure awaits."
A tour guide identified on Facebook as Cyril Tara has been posted photos of Efron, apparently in Papua New Guinea, in recent weeks.
While filming, Efron was reportedly only using basic gear and equipment, a guide partner and camera crew to film the show, which he has been executive producing for his company, Ninjas Runnin' Wild.