Causes of depression are varied: overwork, injury, loss of employment, hormonal imbalance, exhaustion (physical/emotional) and more. One doesn't always know the cause, but it's real.
Depression can range in severity from mild to severe. Symptoms are: depressed mood, diminished pleasure in activities, weight gain or loss, insomnia, loss of energy, purposeless physical activity, feelings of worthlessness, diminished ability to think, indecisiveness, thoughts of suicide, and more.
So how does one deal with depression?
Get a thorough physical check up.
See if there is anything physically going on that could cause a depressive spirit. Check hormones, thyroid, and such like. Check your sleeping and eating habits. Do you exercise? Are meds needed? If so, for how long?
Examine your guilt.
Often, depression and guilt go hand-in-hand. So examine yourself, is there something you need to repent of? Christ's blood covers ALL our sin, just seek it out, repent of it, and be cleansed of it.
Seek help from others, another pastor perhaps, or even a biblical counsellor. They can help you see blind spots, encourage you, pray for you, be a sounding board etc.
Fight the fight.
Know that you are in a battle, depression knocks warriors out of the battle, and can steal your hope, your spirit, and your soul. Don't believe the lies of hopelessness you are being fed. FIGHT!
Read your bible and pray
If you are depressed, take the time to read your bible, to turn to the great counsellor. This is a daily battle, read about others who have fought this battle and won, see their struggles and their winning, the way the Lord sustained them and helped them.
Pour out your soul
Talk to the Lord, tell him your struggles and your needs, your worries and your fears. Confess to him how sometimes you just can't see him, or hear his voice, find things you can praise him for, your health, a bible, a book, a flower.. anything, find it and praise him for it.
A view beyond yourself
Realize that you need to see beyond yourself. Even if you are depressed you can still pray for others, you can still call, visit or write to people.
The bride of Christ
Access the church, attend services, don't withdraw even though you will want to. The Bride of Christ is there for all her people. You need the prayer, support and help from the whole church.
Do your duty
Fulfill your responsibilities as much as you can. Ask God for help if needed. Don't pull away from meaningful work and activities, because if you do so, it only adds to your depression. Rest often, but work as well as you can.
Most of all DO NOT GIVE UP! God can and will see you through this time. Remember that "weeping may tarry for the night, but joy comes in the morning." (Ps 30:5)