What is it supposed to do?

It is not known specifically why Brown went into the chamber, but adherents of the therapy have said it can help muscle soreness and even help people lose weight and look younger.

Does it really work?

Scientists are skeptical. Studies have found very little solid evidence that it helps any conditions. The Food and Drug Administration has not certified its use, and insurance will not pay for the sessions, which can cost $75 for three minutes. A New York Times reporter tried it out in 2017 and said it made her feel “hyper and euphoric.” (She wore proper footwear.)

What are the Raiders saying?

Not much specifically. Coach Jon Gruden said of Brown’s absence: “I think he’s disappointed. We think he’s disappointed. We’d like to get the party started. We’d like to get him out here.” There is no official timetable, and off-the-record reports vary widely over how long Brown will be out.

Has anything like this happened before?

The sprinter Justin Gatlin told TMZ that he had also gotten frostbite from cryotherapy, and it took him months to heal. “It was a disaster. I had, like, boils and blisters all over my ankles,” he said. “Every day I had to get those blisters popped by hand by a therapist. It just got really, really bad.”

Is this the weirdest sports injury ever?

You be the judge.

Glenallen Hill of the Toronto Blue Jays in 1990 suffered cuts and carpet burns after waking up in a fright. “I have a phobia about spiders,” Hill said. “In the nightmare, I was trying to get away from spiders.” The previous year, another Blue Jay, David Wells, suffered injuries related to sleepwalking.