Aerosmith singer Steven Tyler is ailing, and it could be serious. The 69-year-old rock ’n’ roller tweeted Tuesday that he’s headed back to the US for unspecified treatment. The band had played in Sao Paulo Monday night. “I am not in a life threatening condition, but I need to deal with this right away, and get some rest and medical care immediately in order to sustain and maintain my future performances,” Tyler tweeted. “I promise I’ll be back . . . unfortunately health does not wait and it’s something even I can’t schedule around our shows.” As a result, the band is postponing shows in Brazil. Chile, Argentina, and Mexico. Aerosmith has been on what may or may not be its farewell tour. (It’s called the Aero-Vederci Baby! Tour.) Band members have been beset by health issues in recent years. Last year, guitarist Joe Perrycollapsed backstage during a performance in Brooklyn with his band Hollywood Vampires.