This was going to be an uplifting post about a walk-off home run that prevented a disastrous end to what began as a very promising homestand for the Yankees. On precisely one year to the date of his previous game-winning home run, Nick Swisher squared up a 2-and-0 fastball from Orioles closer Koji Uehara and turned a 2-1 deficit into a 3-2 victory.

This was the fourth walk-off victory of the year for the Yankees, who made a habit of these finishes in 2009 with 15. A.J. Burnett got the whipped-cream pie out and delighted the remains of a Yankee Stadium crowd of 44,163 who had not witnessed a scene so familiar last year since May 17 when Marcus Thames clocked Red Sox closer Jonathan Papelbon.

The Yankees were still celebrating among each other when word came out during manager Joe Girardi’s post-game news conference that catcher Jorge Posada was undergoing tests at New York Presbyterian Hospital for concussion symptoms. That he was not in the lineup set off no signals because Posada is often rested in day games that follow night games.

It was not until the seventh inning when Francisco Cervelli batted for himself with two out and runners on first and third and the Yankees trailing by one run that some of us in the press box suspected that Posada was not available at all because this was an obvious pinch-hitting situation.

Jorgie took a foul ball by Nick Markakis off the left side of his mask Tuesday night. He mentioned it after the game to Girardi but did not seem overly concerned until he reported to the Stadium Wednesday and told the manager that he had trouble sleeping because of severe headaches. That’s when alarms sounded, and Posada went through a battery of tests and was sent off to see a neurologist.

This is no Sissy Mary. This is Jorge Posada, who is probably the toughest guy in the room. When he gets hurt, it is usually something pretty serious. Jorgie played a game with a bone fracture in his right foot before going on the disabled list in mid-May.

Concussions are nothing to fool with. The Mets have been without left fielder Jason Bay since July 25 when he collided into a wall at Dodger Stadium. Twins first baseman Justin Morneau suffered a concussion July 7 when he got hit in the head by a knee while sliding into second base and may not play again this season.

At this point, it would appear unlikely that Posada would make the 3 ½-hour flight from New York to Dallas that the Yankees have scheduled Thursday night even if the test results are in his favor. Air travel is one of the worst things for a person with concussion symptoms. The Mets made that mistake last year with outfielder Ryan Church, who never fully recovered from two concussions.

Yankees players were unaware of the Posada situation after Wednesday’s game. It was sobering news to all as well it should be.

“Obviously, we don’t want to lose anyone, and Jorge’s a crucial part of this team,” said Alex Rodriguez, who started the ninth-inning comeback with a leadoff single. “So we have to hope for the best right now.”

The Yankees embark on a 10-day, nine-game trip through Texas, Tampa Bay and Baltimore. The Rangers and Rays are playoff-bound teams, and the Yankees discovered that under Buck Showalter the Orioles have gotten tougher.

“This was an important win for us,” A-Rod said. “To get swept at home is unacceptable.”

Yet it very nearly happened. After sweeping a four-game set from the Athletics and taking two of three games from the Blue Jays, the Yankees needed Swisher’s 26th home run, a jolt over the left-center field fence, to avoid losing three in a row to the last-place Orioles.

Impressive ensemble pitching by the young Orioles staff quieted Yankees bats until Swisher’s blow kept the broom in the closet. Post-game merriment was muted once Posada’s condition became known. The Yankees are headed for the backstretch of their season having to rely on Cervelli and fellow backup Chad Moeller, who a week ago was in the minor leagues.

“If I got to do it, I got to do it,” Cervelli said. “I have been learning a lot here.”

The Yankees are skipping Phil Hughes for a turn in the rotation and will go with Javier Vazquez, Burnett and Dustin Moseley in Texas. They were clinging to the hope that they would not have to skip their catcher as well.