An American climber who fulfilled his dream of climbing the highest mountains on each of the seven continents by reaching the summit of Mount Everest died of probable altitude sickness on the way down, mountaineering officials said Friday.

Don Cash became ill at the summit and was treated there by his two Sherpa guides, one of the officials said.

"He got high altitude sickness on top of Everest," said Pasang Tenje Sherpa, head of Pioneer Adventure, which provided the guides.

"When he was on the top he just fell. The two Sherpas who were with him gave CPR and massages," he said. "After that he woke up, then near Hillary Step he fell down again in the same manner, which means he got high altitude sickness."

Hillary Step is a rocky outcrop near the summit named after Sir Edmund Hillary, who was the first person to climb the mountain along with the Sherpa Tenzing Norgay in 1953.

Altitude sickness is caused by low amounts of oxygen at high elevation and can cause headaches, vomiting, shortness of breath and mental confusion.

Cash, 55, from Utah, had a long-held dream to climb the "seven summits," the highest mountains on the seven continents, his daughter Danielle Cook posted on Facebook on Wednesday.

Santa Bir Lama, the president of the Nepal Mountaineering Association, said Cash's body was still near Hillary Step.

"Many others who are at the summit are still there. When the Sherpas come down, then they can bring his body down," he said.

Pasang Tenje Sherpa said Cash's brother had sent him a message thanking the Sherpa guides, Norbo and Tenzin, for their help.

"Please tell Norbo and Tenzin our family's deep appreciation for their heroic effort to save Don," he quoted the message as saying. "Give them our love and prayers, and we are glad they are safe."

Before he headed for the summit, Cash texted his son Tanner that he felt "so blessed to be on the mountain that I read about for the last 40 years."

Cash said on his LinkedIn page that he left his job as a sales executive to try to join the seven summits club. In January, he wrote, he climbed Mount Vinson Masif, Antarctica's tallest peak.

Cash is survived by his wife Monette and their four children, the Salt Lake Tribune reported.