my parkrun this week was abandoned just after the 3K mark due to a bit of a medical situation. Not for me but for one of the other runners.
I was running along fairly happily (not at PB pace due to the heat) a few metres behind (and catching) another lady as we passed 3K. Then we turned a corner and found another lady flat out, face down at the side of the path, with her dog laying beside her.
The lady I had been about to pass stayed with her whilst I had to sprint off and cut through the park to the finish area to find someone to help.
Fortunately the lady who had collapsed was OK. It's apparently quite common for her to faint during exercise (suffers from low blood pressure apparently) and the heat didn't help. A few minutes of sitting down and some water and she was back on her feet.
But that was my run done. On the plus side, I've gotten my first ever mention in the weekly run report (even if not for the best of reasons) and also made an appearance in one of the run report photos (not sure if that is a plus or not).
Be careful when running in the heat everyone. Especially if you have an underlying condition that could be exacerbated by it. Keep those fluids and electrolytes topped up!