A doctor known for advising people on the risks of Covid-19 got a double surprise: He got Covid, and he wound up needing stitches because of it.

Dr. Robert Wachter, who chairs the Department of Medicine at the University of California at San Francisco, said he had not tested positive for Covid until last week, according to posts from his Twitter account. He said he was fully vaccinated and had received his second bivalent booster in April.

He said his symptoms started with a dry cough on July 9, and by that night, he had a fever, chills and a sore throat. Wachter said he made a mistake the following day when he took a shower while feeling these flu-like symptoms.

"I work (sic) up in a bloody pool on my bathroom floor," he wrote on Twitter. "There was a dent in the lid of a trashcan, likely where my head had hit. I remembered nothing. As I managed to get up, it was clear that my face was going to need stitches, and more than a couple."

Wachter said he required stitches on the back of his head and on his forehead, which he shared in a photo of himself with a black eye. He declined an interview to go into more detail about his illness and recovery.

Wachter became a highly followed doctor on Twitter for sharing his own risk gauging and Covid advice during the pandemic, and he has urged people to get vaccinated. He said his Covid "case is a cautionary tale" and warned people to avoid the shower mistake he made.

"While the instinct to take a shower when you're sweaty and gross is understandable, stepping into hot water when you're dehydrated and flu-ish can cause your blood vessels to dilate, leading to a dangerous drop in blood pressure," Wachter wrote, adding that was exactly what happened to him earlier this week.

He said he was lucky to have his future son-in-law available to drive him to the UCSF emergency room. He was admitted to the hospital.

Doctors sent him for two CT scans and later an MRI, due to the extent of his injuries on the front and back of his head, he said.

He said a head CT scan showed a subdural hematoma, which happens when blood collects between the brain and the skull. A neck fracture appeared in one of his vertebrae in another CT scan.

Wachter's MRI didn't show any additional damage, he said. He added a message of thanks for his colleagues who stitched him back together.

"Luckily, at my age a few scars don't bother me much, and I believe my wife likes me for reasons other than my previously seamless brow," he said.

After 24 hours in the emergency department, Wachter tweeted that he is home and isolating. He said he's taking the anti-viral medication Paxlovid to help lessen the severity and duration of the illness, as well as the chance of long Covid.

As far as future brushes with Covid, Wachter said he doesn't think he will change his behavior, as long as cases remain low. "I'll continue being relatively careful, but no more than I've been," he said.

While he has not treated any Covid patients, Wachter said he wears a KN95 mask in clinical settings. Sometimes he's removed his mask in non-crowded meetings, he added.

"I will, however, be more careful about showering or taking a hot bath or hot tub when dehydrated. That's one important takeaway from this mess," he said.