Nick Swisher hit a walk-off home run yesterday, meaning the Yankees not only avoided a sweep at the hands of Baltimore, but extended their lead over Tampa Bay to two and a half games. (Said Alex Rodriguez: “For us, it’s unacceptable to be swept at home,” though he surely meant “it’s unacceptable to be swept at home by the Orioles, no matter who their manager is.”) But perhaps the best news of the day came after the game had ended. Jorge Posada wasn’t available yesterday — even to pinch hit — because he was suffering from what Joe Girardi called “concussion symptoms.” In fact, he spent the afternoon at New York-Presbyterian Hospital undergoing tests. Luckily, those tests came back negative, and though Posada is day-to-day and may not start the next couple of games, it’s apparently nothing more serious than that. Crisis averted, it seems.