BOSTON – When the carnage was finally over, as the ragged Red Sox left for the West Coast a season-worst 6 ½ games behind the Yankees, David Ortiz summed it up as succinctly as he could.

“This whole thing has been a nightmare,” Ortiz said after the Yankees completed a five-game sweep with a 2-1 victory. “I’m gonna sleep my first three hours [on the plane] and see if I can have another nightmare.”

Just before 2 a.m. yesterday, after a gut-wrenching, 8-5, 10th-inning loss that began Sunday night, Ortiz said he’d never seen the Bombers play this great in the 10 seasons he’s been in the majors.

“It’s like they have a secret weapon every time for every situation,” Ortiz said. “They’re on top of their game.

“I think this is the first time in a long time I have seen the Yankees all compact all the way around. It’s hard to beat a team that is locked in like that.”

After the fifth straight loss, Ortiz vowed to keep fighting, but the landscape is bleak. Boston has 38 games remaining. The Sox – losers of 12 of 16 – just embarked on a nine-game road trip against the Angels, Seattle and Oakland, and they’re a sub-.500 club on the road (30-31).

“We are going through the fire,” Mike Timlin said. “We are going through the low times.

“Character is not built on top of a mountain. Character is built in a valley when you can’t really see it. And that’s where we are right now: We’re in a low valley.”

Timlin said the Red Sox, who have won 95 or more games and been a playoff team the last three seasons, aren’t dead and won’t ever stop battling. But he admitted the club had its confidence shaken by what he called a tail-kicking. And leadoff hitter Coco Crisp, 1-for-19 in the series, said he’s “beating myself up about it.”

Mike Lowell tried to look on the bright side, although he admitted the Sox have dug themselves “a helluva hole.”

“But I think we’ve got to take it in pieces,” Lowell said. “If we can look at it like if we can gain one game a week . . . you can’t look to gain six games in a week, because you’re gonna look to do something that’s impossible.

“But we need a big turnaround, that’s for sure.”

Mark Loretta noted that the game has a way of humbling you when you’re doing well, and bringing you back from the dead when you’re not. He said it was the most physically and emotionally demanding stretch of games he’s ever been a part of.

“It doesn’t get much tougher than that,” Loretta argued.

Actually, the tough part has only just begun.