When we lose someone, it is human to be sad. Loss is a valid reason to become emotional and to struggle with our feelings and thoughts. Joy is not happiness. Happiness is based on our current situation. Joy is based on our attitude. God doesn't tell us be happy when someone passes away but He does tell us to rejoice and to have joy because life is more than our time on this earth and the person who we lost did not die, but has passed away to a better place.
Lord, help me to have an attitude of joy in any situation I may find myself.