Michael Boatwright, 61, woke up with amnesia, calling himself Johan Ek, The Desert Sun reported.
Boatwright was found unconscious in a Motel 6 room in Palm Springs in February. After police arrived, he was transported to the Desert Regional Medical Center where he woke up.
Hospital officials said Boatwright may have been in town for a tennis tournament in the Coachella Valley. He was found with a duffel bag of exercise clothes, a backpack and tennis rackets. He also carried four forms of identification - a passport, a California identification card, a veteran's medical card and a Social Security card - all of which identified him as Michael Thomas Boatwright.
Palm Springs police have documented his information in case anyone lists Boatwright as missing or wanted, authorities said.
In March, doctors diagnosed Boatwright with Transient Global Amnesia, a condition triggered by physical or emotional trauma that can last for several months.
The rare mental disorder is characterized by memory loss, "sudden and unplanned travel," and possible adoption of a new identity, according to the Sun.
After an extensive search, medical personnel and social workers have been unable to locate Boatwright's next of kin. Authorities are still unsure of his birthplace, listed on his identification as Florida. Photos show him in Sweden at a young age.
The Desert Sun reported it had located Boatwright's sister in Louisiana but she was unable to shed any light on what had happened to him.
"I haven't talked to him in years. He just disappeared," Michelle Brewer said Monday in a telephone interview.
Brewer estimated she had last spoken to her brother about 10 years ago and couldn't even get in touch with him when their mother died last year.
"He's always been just a wanderer," Brewer said. "Then he'd come back when he needed some money or something from somebody. Then he'd take off again."
Swedish public records show Boatwright lived in the Nordic country on and off between 1981 and 2003. Several Swedes on Tuesday said they knew of him as an American with a big interest in medieval history and jousting.
Swede Olof Sahlin said he met Boatwright around 1985 through their joint interest in medieval history. He said he saw the American at jousting events regularly in the 1980s and sporadically in the early 1990s.
"He was nice, sympathetic and talented at fighting in plate armor," Sahlin told The Associated Press. "A little bit reserved maybe."
Sahlin said he never knew how Boatwright made a living during his time in Sweden but has now heard from other friends that he briefly worked as a personal assistant and in the construction sector.
Sahlin said their last contact was in 1999 and he doesn't know what happened to him after that.
Boatwright doesn't recall how to exchange money, take public transportation or seek temporary housing like homeless shelters or hotels, the social worker assigned to his case, Lisa Hunt-Vasquez, told the Sun.
He doesn't remember his son and two ex-wives, either.
He has no income or insurance, further complicating his treatment at Desert Regional. And he has little money he can access - only $180. He also has a few Chinese bank accounts but can only access one account, which holds $7, according to the newspaper.
Doctors don't know how much longer he will be able to stay at the center. Aside from his amnesia, Boatwright is in good health. The hospital is currently looking for alternatives that would keep him off the streets. For now, Boatwright is unsure of both his past and his future.
"Sometimes it makes me really sad and sometimes it just makes me furious about the whole situation and the fact that I don't know anybody, I don't recognize anybody," Boatwright told the newspaper.
Last year, a North Dakota college student who disappeared for nearly a week before turning up in Arizona said she had a bout of amnesia and didn't know who she was.
Amber Glatt, 22, a Valley City State University student, vanished on the Fourth of July, prompting aerial searches. She contacted her mother five days later from the Grand Canyon. Her mother said Glatt has had recurring amnesia since suffering a head injury years ago.
Glatt told WDAY-TV that after she lost her memory she met a man in a bar who let her tag along on his trip to the Grand Canyon. She said the man eventually saw online that she'd been reported missing and alerted her.
Glatt regained most of her memory.