I can't imagine seeing stars from intentionally trying to hit myself in the head with a paddle. It takes 60 to 90 Gs to cause a concussion. The physics of a 1/2 pound paddle hitting a 8 pound head makes it very difficult to reach a 60 G threshold. Your stroke was finishing so it was slowing down. Proper follow through does not power through much more than the ball contact.

Getting your bell rung is not really a sound. It is more of a vibratory sense of a chaotic sounds and vision disturbances and mental confussion. Your vision may make things look like they are vibrating back and forth as your eyes try to regain their coordination. Some may experience a tinnitus like sensation but it is not common.