CHICAGO — The toughest part of having COVID-19 for Jayson Tatum wasn’t the headache, the high temperature and chills he experienced. Those symptoms went away after the first night.

Most difficult was the mental toll.

“It was tough, especially your initial reaction once you find out,” he said. “I don’t know if it’s panic. But you definitely worry because of everything you read about it and hear, how many people it’s affected and how many people didn’t make it.”

Tatum scored 24 points after missing five games, Jaylen Brown had 26 and the Boston Celtics beat the Chicago Bulls 119-103 on Monday night.

“The first four days or so, for lack of a better word, it bothered me,” Tatum said. “It was on my mind. I was thinking, do I feel OK, do I not feel OK? Can I smell this? Does my chest hurt? Or am I just overthinking?”

Tatum said he felt a bit tired in the first half. But he got a second wind.

He made three 3-pointers and had five assists over 31 minutes in his first appearance since Jan. 8.

Brown had another solid game following his 33-point outing in Sunday’s romp over Cleveland.

Daniel Theis scored 19 points and Marcus Smart added 13 while tying a career high with 11 assists as the Celtics won their second straight.

Zach LaVine led Chicago with 30 points and shot 6 of 10 on 3s. But he also committed six turnovers, giving him 13 in the past two games.

Lauri Markkanen scored 18. Thaddeus Young just missed a triple-double with 16 points, nine rebounds and nine assists, but the Bulls dropped their second in a row after three consecutive wins.

“They’re all going to need to learn how to win,” coach Billy Donovan said. “I wish I could snap my finger or pour something on it to make it just happen. But it doesn’t work that way. Unfortunately, before you win, there’s generally a lot of suffering.”

Tatum missed five games after testing positive for COVID-19 and hadn’t played since the Celtics’ Jan. 8 win over Washington. He went into isolation under NBA health and safety protocols the next day. The Celtics were 2-3 without him.

Coach Brad Stevens said before the game Monday that Tatum wouldn’t be on a specific minutes restriction.

“He’s not on a minutes restriction per se. We’ll monitor those appropriately,” Stevens said. ”Obviously we’re not going to get into the high 30s or 40s tonight.”

Stevens said the Celtics made a decision not to ask Tatum to play both games of the Sunday-Monday back-to-back series coming off the long period of inactivity. They planned a hard workout Saturday, a day off Sunday and a return Monday against the Bulls.

Tatum emerged from COVID-19 quarantine last Tuesday, passed his physiological tests and worked out in Boston on Wednesday, Thursday, Friday while the team was in Philadelphia before Saturday’s simulation.

He had been averaging 26.9 points and 7.1 rebounds per game before that.

NOTES: The Celtics held out guard Kemba Walker. The four-time All-Star played the previous four games after missing the first 11 because of a left knee injury. … Bulls center Wendell Carter Jr. (bruised right quadriceps) will be evaluated toward the end of the week after he missed his third consecutive game. Coach Billy Donovan said Carter is improving, though he hasn’t been participating in any on-court activities. The Bulls are off until Portland visits on Saturday. Their game at Memphis on Wednesday got called off because of the Grizzlies’ COVID-19 issues.

UP NEXT?: Boston is scheduled to play at the San Antonio Spurs on Wednesday. Whether the Celtics actually make that trip was up in the air after Monday’s game between the Spurs and Pelicans was postponed because the NBA determined neither team would have enough players available. “My thought would be we should not fly there until we know. That’s the bottom line. That’s my only thought going through my mind with all the travel we have coming up,” Stevens said.