Emotions are based on whats going on around us. Happy, sad, angry.
Joy from God is not based on the world around us.
When life gets tough, when we depend on God, know He is in full control of the world and whats happening in our lives, when we trust in Him, we can know His joy. Jesus said we would have peace that surpasses all understanding, with that peace comes the joy of knowing Him, and that He controls the universe,and loves us no matter what the tough times are like.
I do speak from experience.
Four years ago this month my son was arrested while I was on the phone with him. A plea and sentencing took 6 months, during that time I lived with the fact (fear, terror) if they did not give him concurrent sentences he could possibly be in prison the rest of my life. He was 19 at the time.
God was good to us all. He was sentenced to 6 years, and served 2, he is now married and has a daughter and lives just fine without his old life.
And thats about all I can say about it. So no questions about my son.
Yes we can experience joy in the worst of times. But it does not mean we also do not have down times. It means we don't live in the down times, they do not command and control our lives. Many times Christians mistake joy for being happy go lucky all the time, smiling no matter what, never a bad mood. but the joy that comes from God goes much deeper then that.