thermal shock

it had been so hot these last few days that i thought the lake must have warmed up again after last week's cold spell. well, maybe not. 18°C was, as i discovered once i got into it, just as cold as it sounded. once i got swimming, it was fine, but i was really cold thereafter, despite the warmth. a whole hour later, back at the very hot office, i felt nice and cool, when i knew i was supposed to die of heat...