After years of hearing roommates, family members and others complain about his notably loud snoring patterns, Hansen entered a sleep-study clinic and discovered he had sleep apnea.
That was the winter following the 2006 season. Hansen kept the news to himself for a while, but he was suddenly confronted with it head-on by his bosses.
You see, when the Red Sox held their Rookie Development Program in January 2007, club front office members didn't appreciate Hansen falling asleep during some of the lectures.
It was then that Hansen told the organizational brass what was going on.
"They brought me into the office and they were like, 'We see you dosing off in the meetings.' I was like, 'I went to a sleep center and they said I have severe sleep apnea. They said I have 56 currencies in an hour.' That's 56 minutes where I'm not sleeping comfortably," said Hansen.
Hansen estimates that on nights he thought he was sleeping for eight hours, he was really only getting about two actual hours of sleep.
He chose not to get surgery to correct the matter last year because the recovery time would have interfered with his preparation for the 2007 season. As it turns out, Hansen spent the entirety of that frustrating season in the Minor Leagues. For a man who spent time in the Major Leagues in both 2005 and '06, this was clearly a step back.
One will never know exactly how the sleep apnea affected Hansen's pitching or workout routines. But the problem has been corrected. Hansen underwent the procedure from Dr. Mack Cheney at Massachusetts Eye and Ear Infirmary in November and now feels like a new person. Though the procedure prevented Hansen from working out until January, he feels like he is on course to have a normal Spring Training.
"[The surgery] went really well," said Hansen, who worked out with some of the other early birds on Tuesday, two days before pitchers and catchers report. "They took out my tonsils and deviated septum. It makes me able to breathe a little bit easier and sleep a lot better. Now I'm able to get a full night's sleep and wake up in the morning and feel replenished and everything.
"When I did the sleep study last season, they said I had 56 currencies in an hour, and the normal amount is four. They said I pretty much didn't sleep at all. I basically had no clue until I woke up the next morning and still felt tired."
"Oh, it feels great," Hansen said. "I'm able to wake up. Right now, I'm able to just get right out of bed. I woke up at 6 o'clock this morning. I just got right up and had nothing else to do, so I came [to the ballpark]. I'm not going to sit around the house. I might as well go do something. It feels good to wake up and now feel replenished."
Perhaps that burst of energy is what Hansen needs to win a spot out of the Boston bullpen and at last live up to some of the expectations placed upon him when the Red Sox made him a first-round pick in the 2005 First-Year Player Draft. Hansen was a stud closer at St. John's, backed by a wicked slider.
The Red Sox gave him a Major League deal out of college for four years at $4 million, something very rare for a Draft pick.
Hansen is hoping to make his breakthrough this year. Though it seems like he's been around for a while, Hansen is still a young man at 24 years old.
And the Red Sox, who didn't make any significant additions to their bullpen over the winter, hope that Hansen can basically serve as a key acquisition.
"He's a big part of our Spring Training this year," said Red Sox pitching coach John Farrell. "He's still a key component for our bullpen and the long-term success we'll have here. Pitching is a game of attrition, and we know we're going to need more than the 12 guys that we begin the season with, whether he's part of that initial 12 or not. But he's got all the physical abilities in which he was drafted under. It still gives everyone a strong belief that he's going to be a key contributor for us."
And Farrell doesn't doubt that the sleep apnea had at least some effect on Hansen's inconsistency.
"I'm sure that has had a negative impact on his performance in the past," Farrell said. "If there are days you feel like you have greater energy than others, that's surely going to physically affect you when you get on the mound on a given day."
While Manny Delcarmen and Hideki Okajima figure to be Jonathan Papelbon's top two setup men, Hansen could pitch himself into playing a key role.
Did the pressure of being such a high Draft pick do anything to diminish Hansen's performance?
"I wouldn't say I put too much pressure on myself," Hansen said. "I think I might have taken stuff for granted. I wasn't working on my mechanics as I should have. That's one thing I learned, and I learned it the hard way. Now I'm basically going back, getting my routine going, working on my mechanics and doing the stuff I have to do. I've matured a lot."
The biggest key for Hansen will be to regain that slider that made him a seemingly "can't miss" prospect coming out of college. Hansen thinks the pitch is back.
"It's a lot better. It's got more bite to it," Hansen said. "[Triple-A pitching coach] Mike Griffin was able to help me out at Pawtucket with that [in 2007] and we worked on that every day. Now I have that pitch, as opposed to not having it at all."
As for sleep apnea, Hansen said, "They say it's pretty common, but not for a guy my size. Mostly it's for people that are pretty much overweight."
Hansen has never had a weight problem -- just the weight of expectations. But now that he's fresh, this could be the year he arrives as an impact reliever.
"Right now, I feel like I have a lot of energy. I feel like I could do a lot of things that I couldn't do before," said Hansen. "I got the [surgery] done, so now is the season to look forward to. Right now, I'm about to go run and I feel like I can, instead of going out there and running and feeling tired and calling it quits after that."
When the Red Sox won the World Series last year, Hansen was just another envious Minor Leaguer.
"It was great to see them accomplish the great season that they had," Hansen said. "Once I saw them playing like a team, I was like, 'They got it.' You see that in every team that wins championships. You see them all of a sudden just form as one. They know what their jobs are and they go out and do it. That's pretty much it."
And if there's another victory celebration this October, Hansen hopes he's in the pile.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.