"The joy of the LORD is your strength." Nehemiah 8.9. There is a time to be joyful as an act of will if it is not happening naturally. It will give you a lot of strength and help you regain your footing in faith again.
Spending too much time in a negative state is a trap, and unwholesome. One of Satan's tricks to pulverize a Christian's faith is to keep him inward looking and focusing on what he is whispering. For your survival you need to get out of that rut.
There are many ways to be joyful or cheerful unique to each of us. There are hobbies to pursue. Draw, paint, write, read, play indoor games, meet with family, meet other Christians, meet with friends, relax, go swimming, running, enter a sports event. By filling the mind with a lot of things to do, we can be proactively joyful. With the Holy Spirit's leading.
Being joyful induces hope and brings faith alive. It casts off burdens. You are actively working with God for your own peace and restoration. Be strong in your faith by being joyful. When Satan sees you being joyful, he backs off.