CHICAGO (CBS) — Police Supt. Eddie Johnson told Mayor Lori Lightfoot he had been drinking at dinner before driving early Thursday morning, and pulling over near his home and falling asleep behind the wheel, sources told CBS 2’s Brad Edwards.

Johnson told reporters he had a mix-up with his blood pressure medication, and felt he might faint as he was driving home from dinner, so he pulled over to rest not far from his home in Bridgeport. Johnson said he fell asleep when he pulled over.

A woman who saw Johnson in his Chevy Tahoe called 911 to report seeing someone asleep at a stop sign, according to CPD spokesman Anthony Guglielmi. When officers arrived at the scene, they did not see any signs of impairment.

Responding officers also did not administer a field sobriety test – rather, they let their boss drive home. Johnson later requested an investigation by the Internal Affairs Division.

Sources said Johnson admitted in a conversation with the mayor later on Thursday that he had “a couple drinks” before he was found passed out behind the wheel.

CPD spokesman Anthony Guglielmi said he could not confirm or deny whether the superintendent told the mayor he had been drinking before the incident.

“While we have no indication of impropriety at this time, this question can only be answered by the internal affairs Investigation. That investigation active and ongoing,” Guglielmi stated in an email.

Department rules prohibit police officers from drinking alcohol while on duty or in uniform, but it was not clear if Johnson was in uniform at the time.

On Friday, Mayor Lori Lightfoot told reporters Johnson called her later Thursday to tell her what had happened, but she declined to say whether she believed it was proper for Johnson to be allowed to drive himself home.

“There’s an investigation that will sort out the specifics, but I’m going by what he informed me of,” the mayor said. “We’ve all had moments where we’ve been driving, and we might have felt something. I think he took what he believed was the appropriate precaution based up on what he was feeling.”

Lightfoot said Johnson told her that he’d been to the doctor earlier in the week regarding his blood pressure, and felt ill while driving home, so pulled over to the side of the road.

“It was the right thing to call for an investigation. That investigation will play itself out,” she added. “Everybody, whether it’s the superintendent or a beat patrol officer, has to abide by the rules, and there’s an investigation that’s open, and we’ll see how that plays itself out.”

Johnson said Thursday night that he would have been better off having a driver with him after going out for dinner on Wednesday, but both he and his usual driver had already worked all day. Because the driver has a young family that includes a student in the Chicago Public Schools where teachers are now on strike, Johnson let the driver go home.

Johnson added that he had visited his cardiologist twice earlier in the week to follow up on a blood clot that he experienced this summer.

“When I visited him on Tuesday, he adjusted my medication. It’s painful to admit this, but when he adjusted my medication, I took the old medication out for high blood pressure, but I failed to put the new medication in,” Johnson said. “So he wasn’t too happy with me today when he found out I hadn’t taken it, and I actually had forgotten to put it in there. So because of last night’s episode, I then visited my neurologist earlier today, and discovered I had elevated blood pressure – and that’s when I realized, I then switched the medications out.”

Johnson clarified that he had thrown away his old blood pressure medication when his cardiologist switched his prescription, but forgot to take the medication altogether on Wednesday rather than taking the new medication he had been prescribed. He said he needs to do better with his blood pressure medication.

After the incident early Thursday, Johnson visited his neurologist, who recommended that he go to the emergency room to get checked out.

“I assured him – we fought on the phone for a little while – that I would go, but I just felt it was incumbent on me to be here tonight for the Police Board meeting,” he said.

Meanwhile, Johnson said: “To avoid the appearance of impropriety and just have total transparency, I ordered the Bureau of Internal Affairs to conduct an internal investigation just to be transparent. As I’ve said before, every officer, regardless of rank, must uphold themselves to the highest of standards, and that includes me.”

A reporter asked Johnson why responding officers had not given him a Breathalyzer in the interest of transparency. Johnson said officers do not give Breathalyzer tests “just because” – only if there is probable cause such as someone looking impaired or smelling of alcohol or cannabis.

Guglielmi said Johnson went to Rush University Medical Center after speaking Thursday night at Police Headquarters. He was released around 2 a.m. Friday, with doctors’ orders to “take it easy.”

Johnson has had a series of health issues since taking the top post at CPD. In June, he was treated for a small blood clot that was found in his lung during a routine test.

In August 2017, he received a kidney transplant from his son. He fainted at an awards ceremony a few days after returning to work that October, after suffering a blood pressure issue.

When he fell ill at the news conference 2017, spokesman said he had taken blood pressure medication on an empty stomach and felt sick, but the issue was not related to his kidney disease.

Johnson was diagnosed with kidney disease more than 30 years ago.