It greatly depends on what apps you have installed and open.

Really? I hope it doesn't happen to me. Do you know if Note II users have reported the same problem? I get so upset when these things happen because I'm new to this phone and I sure wouldn't know what to do . Thanks for the helpful information!

Apparently this happens when you mute the volume in an app. That app then takes control of the media volume.
The only way around this is to close that app - open the task manager by holding down the home button and close all active apps. The media volume should return to normal.