Q: Why does my 6th gen nano spontaneously lose sound?

I wear the nano in a wristband when I run/exercise and any song could be playing and suddenly the sound just decreases down to no sound.  And after I attempt to adjust/turn the volume back up, the sound decreases to nothing.  I've tried to reset the ipod, turn off/on and it still doesn't function properly.  Why does this happen?  I've read that it could be because it is overheated because it is too close to the body however it is in a watch cradle so it isn't even touching my skin.