Can you get long-term amnesia from a concussion?

[JackArmentrout]

Hi. Someone I know fell down the stairs and hit his head. He passed out. When he woke up, he was in the hospital (his sister found him and brought him there or called an ambulance, I'm not sure which). They diagnosed him as having a concussion. They also discovered that he'd lost six years of memory. In other words, he couldn't remember anything about the six years of his life leading up to the concussion. He thought he was in England, because that's where he had been living six years ago. In fact, he was in California.

The ER doctors sent him home later that day, explaining that within a few days, his memories of recent years would probably return.

Okay, that's the story he told me. This is someone I hired to do some work for me. The event happened on the day before the work was due. Everyone I know is deeply concerned about this guy, and I feel like a jerk, because I'm skeptical. I feel like it might have been a ploy to get out of doing the work. I know that would be a pretty extreme bit of conning, but sometimes people do extreme things to get out of getting in trouble for not doing work -- or for attention.

I realize no one can know the truth without examining the guy, but I want to know if my suspicions are at least grounded in medical science.

So...

1) How likely is it for someone to lose six years of memory via a concussion? From googling, I have learned that post-concussion amnesia usually is confined to a few hours of memory loss.

2) How likely is it that any reputable hospital would discharge someone the same day as they sustained a head injury severe enough to cause that amount of amnesia?

Everyone is rallying around this guy, and I would be a major pariah if I in any way suggested he might be faking it. I feel like an asshole that I even think it's possible. On the other hand, I can't stand the though that, if he is faking it, he's taking advantage of the sympathies of many good people -- not to mention of the business contract I had with him. It's only been two days since the accident. I have a feeling that in a week, he'll suddenly be all better. Which gibes with what the doctors "said." That he'd likely get all six years of his lost memories back in a few days after the accident.

Thanks for your help!