FFS took him for a walk today about 2pm, quite a hot day but not as hot as other days in the summer. Did not let him swim as usual which was a huge mistake, did not cool down and got high temperature 41C.
On the way back home, close to our house he could not move at all his back legs. My mate ran quickly to my place, got 2litres of water, gave him some and pour the rest on him to help cooling down. 15 minutes later still could not move, panting did not help him a lot, called the vet and went there. He's now admited into for the night since 4pm, being under lots of fluids straight into his blood, ice cooled and wet towels.
Heard from the vet about 2 hours ago, he's a lot better, moving around, should be back home tomorrow. Cost: £250.40. Vets rip you off these days...