The following prayer is attributed to St. Ignatius Loyola (1491 – 1556), the founder of the Society of Jesus. I have found it called both a Prayer for Trust as well as a Prayer When Depressed.
O Christ Jesus, when all is darkness and we feel our weakness and helplessness, give us the sense of Your presence, Your love, and Your strength. Help us to have perfect trust in Your protecting love and strengthening power, so that nothing may frighten or worry us, for, living close to You , we shall see Your hand, Your purpose, Your will through all things. Amen.