The most emotionally complex moment of the 1993 movie “Groundhog Day” arrives midway through the film. It depicts a slovenly Bill Murray, dressed in an undershirt and trenchcoat, as he sits at a diner beside his love interest. By this point, he had relived the same day — Feb. 2 — dozens of times and felt trapped, but also strangely God-like. “I have been stabbed, shot, poisoned, frozen, hung, electrocuted and burned,” Murray related in the diner scene. “And every morning, I wake up without a scratch on me, not a dent in the fender. I am an immortal.”

It’s meant to be a funny scene. A waitress stands nearby, mouth agape, watching in stunned disbelief as Murray considers his predicament.

But to those afflicted with perennial déjà vu, there’s little humorous in what Murray describes. About 60 percent of the population has experienced déjà vu at some point. For almost all of them, it arrives as quickly as it disappears. A flash of familiarity — Have I been here before? — then, poof, it’s gone. But for an extremely small percentage of those who experience déjà vu, that’s not true. For them, it’s an everyday thing.

And then, there’s this: One 23-year-old British man, according to the Journal of Medical Case Reports, has been trapped inside what he calls a “time loop” for eight years. For him, this isn’t just déjà vu, which one study defines as a “memory-based illusion” resulting from the “erroneous activation” of “feelings of familiarity.” He actually thinks he’s reliving past experiences: “Rather than simply the unsettling feelings of familiarity which are normally associated with déjà vu, he complained that it felt like he was actually retrieving previous experiences from memory — not just finding them familiar,” the Journal wrote. It’s a subset of déjà vu called déjà vécu, which translates to “already lived through.”

No one’s quite sure why he feels this way. His physical symptoms aren’t like those of others who suffer from perennial déjà vu because — well, because he doesn’t appear to have any. The most common conditions believed to cause severe déjà vu are neurological, such as temporal lobe epilepsy and dementia.

That was, at least, the case with an 80-year-old Polish man New Scientist called “Mr. P.” Mr. P had a big problem. He didn’t watch TV or read the newspaper — he had seen everything before. The same went for the singing birds. When he walked, the birds all crooned the same songs every day. And when Mr. P’s doctor told him he should get to a memory specialist, Mr. P demurred. He was positive he had already been to a memory specialist.

Mr. P’s problem was neurological. He had dementia. But it’s a very different situation with this anonymous 23-year-old. He’s passed neurological tests with flying colors. So what could possibly explain what the medical report calls his “debilitating déjà vu”? The leading theory: It’s something psychological. The man is wracked with anxiety that may suggest a “possible link” to déjà vu, though one has never been fully studied.

“Most cases like this occur as a side effect associated with epileptic seizures or dementia,” psychology expert Christine Wells of Sheffield Hallam University told the Telegraph on Tuesday. “However, in this instance it appears as though the episodes of déjà vu could be linked to anxiety. … If proved, this could be the first-ever recorded instance of psychogenic déjà vu, which is déjà vu triggered by anxiety rather than a neurological condition such as dementia or epilepsy.”

Anxiety has always been with the 23-year-old — even before déjà vu was. “He had a history of feeling anxious, particularly in relation to contamination, which led him to wash his hands very frequently and to shower two to three times per day, and his anxiety worsened around the time he began university” in 2007, the journal said.

His nerves got to be too much while he was at school, and he soon took a break. That was when déjà vu struck. “His recollection of these early episodes was that they would last for minutes, but could also be extremely prolonged,” the paper said. “For example, while on holiday in a destination that he had previously visited he reported feeling as though he had become ‘trapped in a time loop.’ He reported these experiences as very frightening.”

He went to see doctors, but they couldn’t figure out his condition — everything checked out neurologically. Meanwhile, as doctors grasped for answers, his symptoms worsened. By 2010, he had given up on reading newspapers and watching television — just like Mr. P. — convinced he had seen everything before.

So, can the 23-year-old break free of the time loop? Researchers think the best way to spring him loose would be to treat his anxiety. His condition has created a feedback loop in which bouts of déjà vu incite moments of severe anxiety, which then lead to other episodes of déjà vu.

“Our case is aware of the abnormal familiarity of his memory, and is in fact greatly distressed by it,” author Christine Wells wrote. “This suggests two dimensions … awareness and distress.”