I think some people are just built different…
https://en.wikipedia.org/wiki/Gu%C3%B0laugur_Fri%C3%B0%C3%BE%C3%B3rsson
During the sinking of their boat, off the coast of Heimaey in Vestmannaeyjar, Guðlaugur and two out of four other companions climbed on to the keel. After about 45 minutes, they swam towards the shore, yet the other two disappeared within 10 minutes. The only survivor of the crew of five, Guðlaugur swam for five to six hours in 5–6 °C (41–43 °F) water the 6 km (3.7 mi) to the island, wearing a shirt, sweater and jeans,[1] guided by a lighthouse.[4] He remained clear-headed throughout.[1]
Reaching the shore of Heimaey, Guðlaugur found himself at the most dangerous section of the island’s coastline, due mainly to the waves hitting the coastal lava rock formations. After searching for and finding a suitable, flatter part of the shoreline, he finally got to land but had to walk with bare feet, traversing 3 km (1.9 mi) of volcanic scree.[4] When he knocked on a door at 7 a.m., nine hours after the boat had sunk, he was taken to the hospital. Guðlaugur’s body temperature was below 34 °C (93 °F) yet he showed almost no symptoms of hypothermia or vasodilatation, only of dehydration.[2][3]