There’s no better escape from extreme summer heat than a trip to the beach, but one Massachusetts mother is warning that sunny shorelines can hide dangers.

Heather Cassini, 40, was visiting Hampton Beach with her family on July 4 when her 10-year-old son, Declan, suddenly said he felt unwell. At first, Cassini assumed the heat or ocean waves were to blame. As they headed back so he could rest, Declan became disoriented, collapsed, vomited, and drifted in and out of consciousness.

Pregnant and panicked, Cassini tried to help as nearby beachgoers rushed in. Several nurses assisted until paramedics arrived, checked his vitals, and worked to keep him conscious and warm. After a wait, Declan stabilized and was taken to the car.

Doctors later determined he had developed hypothermia from prolonged exposure to cold ocean water. Cassini hopes the incident warns others that cold shock can strike on summer days unexpectedly.