It was a Sabbath evening nearly 300 years ago when young David Brainerd wrote this in his journal:
Lord’s day, Dec, 16. 
Was so overwhelmed with dejection, that I knew not how to live. I longed for death exceedingly: my soul was sunk into deep waters, and floods were ready to drown me. I was so much oppressed, that my soul was in a kind of horror; could not keep my thoughts fixed in prayer, for the space of one minute, without fluttering and distraction; and was exceedingly ashamed, that I did not live to God. I had no distressing doubt about my own state; but would have cheerfully ventured (as far as I could possibly know) into eternity.
While I was going to preach to the Indians, my soul was in anguish; I was so overborne with discouragement that I despaired of doing any good, and was driven to my wit’s-end; I knew nothing what to say, nor what course to take. But at last I insisted on the evidence we have of the truth of Christianity form the miracles of Christ; many of which I set before them: and God helped me to make a close application to those who refused to believe the truth of what I taught them. Indeed I was enabled to speak to the consciences of all, in some measure, and was somewhat encouraged to find that God enabled me to be faithful once more.
Them came and preached to another company of them; but was very weary and faint. In the evening, I was refreshed and enabled to pray and praise God with composure and affection; had some enlargement and courage with respect to my work; was willing to live, and longed to do more for God than my weak state of body would admit of.
I can do all things through Christ that strengtheth me; and by his grace, I am willing to spend and be spent in his Service, when l am not thus sunk in dejection and a kind of despair.
This great saint, the minister and missionary who spent himself in service to God and Native Americans, also struggled with bouts of depression, which is evident in reading his journal. If you are reading this, dear Christian, and you can relate, be encouraged, as Brainered was, by the promises of God for the support of his precious saints. And know that you are not alone. (HT: Victor McKinnon)