From today's paywalled story in The Athletic on Nimmo (had something like this happen to me once when in my 30's, and it never happened again):
"Nimmo said that doctors told him that what most likely happened was that the cramp spiked his blood pressure and got his heart rate up quickly. He also had a tingling in his hands and felt hot just before fainting.
“I asked them if there was anything I could do to prevent this from happening again, and they said, no — sometimes a perfect storm happens,” Nimmo said. “From what I understood, your brain, when you go back and your blood pressure drops, your brain just loses the blood for one second, and you’re out.” "
"Nimmo said that doctors told him that what most likely happened was that the cramp spiked his blood pressure and got his heart rate up quickly. He also had a tingling in his hands and felt hot just before fainting.
“I asked them if there was anything I could do to prevent this from happening again, and they said, no — sometimes a perfect storm happens,” Nimmo said. “From what I understood, your brain, when you go back and your blood pressure drops, your brain just loses the blood for one second, and you’re out.” "
Mets' Brandon Nimmo says he's OK after fainting, hitting head in hotel room
Doctors told Nimmo that what most likely happened was that a cramp prompted his blood pressure to spike.
www.nytimes.com