Southside Johnny, the iconic lead singer of the rock band Southside Johnny and the Asbury Jukes, was briefly hospitalized after becoming ill during a show in Monmouth County on Saturday. The band was the headlining act for the Stone Pony’s sold-out 50th-anniversary concert in Asbury Park when the ailing singer left the stage. Saturday’s show was the band’s second of back-to-back performances at the legendary venue. The singer, whose real name is John Lyon and is regarded as “the grandfather of the New Jersey sound,” was treated for dehydration at a local hospital after walking off the stage, a…