“I had no idea that this could happen.”

A Massachusetts mom is issuing a PSA for parents after a frightening day at the shore.

“I’m still shaking,” Heather Cassini tells TODAY.com.

In a now-viral Facebook post, Cassini, 40, shared that she was visiting New Hampshire’s Hampton Beach on July 4, when her 10-year-old son, Declan, announced he was feeling nauseated.

It was a hot and humid day, and Declan had been in the ocean playing. Cassini wasn’t concerned, and figured he needed to rest in the shade.

“I thought the breakfast was just too much for the waves and he just needed to lay down,” Cassini wrote. Then, Declan became “disoriented,” and collapsed, landing directly on a dozing sunbather.

Declan was able to pull himself up, but moments later, he stumbled and was back on the ground.

“I’m pregnant and frantically trying to pick him up,” she recalls. “He’s going in and out of consciousness and vomiting. And he was so pale.”

That’s when Cassini says a group of women swooped in to help. One flagged down a lifeguard, another called 911.

“God bless all the people around us. There were so many nurses,” Cassini says

Paramedics determined that Declan had hypothermia from the 52 degree water.