WASHINGTON -- At around 5:15 a.m. on Monday, Brandon Nimmo awoke in his Pentagon City hotel room feeling queasy. As he went to the bathroom to remedy the situation, he began experiencing muscle cramps -- likely the result of a long, humid day at Citi Field. He went for a sip of water.

The next thing he knew, he was lying facedown on his bathroom floor, bleeding onto the edge of a towel.

“I was confused,” Nimmo said. “I was like, ‘Why am I here?’”

So began a frightening episode that resulted in Nimmo spending most of the day in a local hospital, undergoing a battery of tests to determine why he fainted. The good news: A CT scan, an EKG and other tests came back negative. Nimmo is fine, save for a cut on his forehead from where he fell.

But Nimmo, weak from lack of sleep and going the entire day without eating, was out of the lineup for Monday’s series opener against the Nationals and unavailable off the bench. He hopes to return on Tuesday.

“I’ve never fainted,” he said. “There’s never been a moment in my life that I, like, cannot get back. It’s a weird feeling.”

After a few minutes working to stop the bleeding on his forehead, Nimmo called Mets trainer Joe Golia, who came to his room and brought him to the hospital. Golia subsequently contacted manager Carlos Mendoza, who woke up to the unnerving news that his starting left fielder had fainted in the middle of the night.

“It was pretty scary there in the beginning,” Mendoza said.

Nimmo does not know exactly why he lost consciousness. Doctors believe the muscle cramp he experienced while going to the bathroom likely spiked his heart rate, which had been extremely low while he was sleeping. That, combined with a surge of anxiety because he was not feeling well, could have caused a temporary loss of blood flow to his brain.

“It could happen one time in your life and you could never have to deal with it again,” Nimmo said. “I asked them, ‘Is there anything I can do to prevent this from happening again?’ And they said, ‘No.’ Sometimes, a perfect storm happens. What I understood is … when the blood pressure drops, your brain just loses the blood for, like, one second. And you’re out.

“It probably wasn’t very long that I was out. But long enough to fall and do a little bit of damage.”

Nimmo said the issue is almost certainly unrelated to the concussion tests he underwent in mid-June, weeks after being hit in the helmet with a pitch. It was, by all accounts, a freak accident that should only cost him one game.

One of the Mets’ most durable players over the last three seasons, Nimmo has appeared in 380 of a possible 406 games since 2022. He is batting .247/.367/.448 this season with 13 home runs, five stolen bases and a team-high 53 runs scored.

Jeff McNeil shifted to left field in Nimmo’s absence on Monday, with Harrison Bader playing center and Tyrone Taylor in left.