This isn't a normal expression. To 'count down' means to say 10, 9, 8, 7, 6 and so on.The only time you might say 'Count me down' is perhaps if you are preparing to do something, like diving, and you are asking the other person to 'count you down' to zero, at which point you would jump. This doesn't seem likely, though.
As for the lyrics of the song you quote, they don't make any sense to me either.