Here is a command to reload the unity desktop notification panel, in Ubuntu, without restarting the entire system:
:~$ killall unity-panel-service
As soon as the process is killed, a new one will be spawned, refreshing the notification panel. This is useful if you have duplicate icons from frozen apps in the panel.
Sando George is a web development freelancer and a budding Computer Science researcher. He also serves as the CTO of Social Capital Holdings, a startup company dedicated to raising funds for charitable and socially responsible organizations.