When life is too tired and I felt so worthless, I tried my best to read Quran. It's the least I can do when my body and soul have no desire to live anymore.
People don't want to relate the mental illness with someone's faith. But, truthfully I doubt my imaan all the time. My sinful acts, my least prayers, my weaknesses and everything that show that my imaan is just less than others. My good deed is nothing.
So, I'm trying my best to keep it. The least amount of imaan that left in my heart. The only thing that keep me survived. Put trust that Allah will forgive me. He will bless me with goodness and paradise because He is The Most Gracious and Merciful. I wish even I don't have anything that deserve me the Jannah other than trying my best to keep living this life.