8:51 PM PT -- A rep for Santana tells us the 74-year-old was overtaken by heat exhaustion and dehydration, leading to the medical episode. He was taken to a local hospital for continued observation, but his rep says he's, "doing well."
A scary moment for Carlos Santana and his fans, as the legendary musician collapsed onstage during one of his concerts.
Santana was performing at Pine Knob Music Theater, outside Detroit, Tuesday night, when a concertgoer tells us the medical emergency happened. We're told Santana was bout 4 or 5 songs into his set, and started to sing a song called "Joy."