Los Angeles Chargers head coach Jim Harbaugh has spoken out about a health issue that caused him to abruptly leave the sidelines mid-game.

Harbaugh, 60, entered the Chargers' medical tent just before kickoff of the team's Sunday, Oct. 13, showdown against the Denver Broncos. As the game began, the coach was seen walking toward the locker room with team staff.

The Chargers' X account reported that Harbaugh left with an “illness” and it was “questionable whether he would be able to return.”

Minutes later, however, Harbaugh returned to the field and remained there for the remainder of the Chargers' 23-16 victory.

During the CBS broadcast sideline reporter AJ Ross said Harbaugh was struggling with “arrhythmias,” which Ross reported Harbaugh had “been struggling with off and on for a while.”

Read on for a full breakdown of what Harbaugh said after the game, the exact nature of Harbaugh's condition, and how those closest to Harbaugh reacted to the news.

Why did Jim Harbaugh leave the field against the Broncos?

After Harbaugh suddenly and without warning left the field on Sunday, he explained exactly what happened during his postgame press conference.

“Everything was fine in the end,” Harbaugh told reporters. “I'm dealing with this, I think, minor (problem) called atrial flutter. I got into an episode with it today. The doctors examined me and I returned to sinus rhythm, the normal rhythm. So I came back.”

Harbaugh was having “some erratic swings,” so he wanted to get checked out by the Chargers’ training staff.

“I know a lot about it, so I just wanted to see what the pulse was,” Harbaugh said of his trip to the medical tent. “I'm not good at taking my own pulse. So they just took the pulse and it was the arrhythmia. But I felt like we were fine, and then they just said, 'No, we need to do an EKG.'”

Harbaugh added: “Then I came back to the locker room and the paramedics came and did an EKG. They said it was back in sinus rhythm and I said, ‘I’m fine.’ So I’m back out there on the field.”

What is atrial flutter?

According to the American Heart Association, atrial flutter is a rhythmic disorder of the heart that occurs when “the ventricles beat faster than normal and not always in a coordinated manner.”

During atrial flutter, the upper chambers of the heart beat 250 to 350 times per minute, a dramatic increase from the usual rate of 60 to 100 beats per minute.

Although the cause is largely unknown, atrial flutter can lead to stroke, heart failure and other cardiac arrhythmias.

Does Jim Harbaugh have a history of heart problems?

Yes, Harbaugh underwent cardioversion to correct an irregular heartbeat in 2012 when he was acting head coach of the San Francisco 49ers.

“Get it back to normal,” Harbaugh told reporters at the time. “It’s amazing that they can do a procedure like this.”

Cardioversion is an electric shock that returns the heart to a normal rhythm.

In 1999, Harbaugh underwent a similar procedure to correct his heartbeat while playing for the Chargers.

During his postgame press conference on Sunday, Harbaugh vividly recalled the most recent incident, which occurred during a 32-7 49ers victory over the Chicago Bears.

“I always remember this in 2012, it was during the Monday night game,” Harbaugh said. “Colin Kaepernick and the 49ers against the Chicago Bears. Colin had a great night that evening. There was nothing during the game. After the game I was examined and ended up having an ablation because it didn’t get back into rhythm.”

Harbaugh had a good sense of humor during both exams, joking, “2-for-0 with cardiac arrhythmias.”

How did Jim Harbaugh's family and players react to the cardiac arrhythmia incident?

Jim's brother, John HarbaughBaltimore Ravens head coach, was escorted out of his postgame press conference on Sunday after learning the news.

During his media appearance on Monday, October 14, the 62-year-old Ravens coach addressed the incident.

“He has had this problem in the past and has had several procedures over the years,” John said. “He also had it once as a player. He is fine now and will do some tests today.”

John joked that (Jim) “somehow convinced” the medical staff to let him back on the field to practice for the rest of the game.

Chargers quarterback after Sunday's game Justin Herbert praised his coach's stoicism given the circumstances.

“He’s tough,” Herbert, 26, told reporters. “He hid it really well because I didn’t know. They did a good job of keeping calm.”

The Chargers return to action on Monday, October 21st against the Arizona Cardinals.