If you have suffered from clinical or chronic depresssion it is probably too much to ask that you will never ever again have a problem with depression.
And if you are familiar with depression you know exactly when it is coming on. I feel the key is not to let it get its grip on you. If you let it get a hold on you it will be that much tougher to alleviate the problem.
So what do you do? Anything. Something. Just do not do what you have been doing. The enemy of depression is activity. Friends of depression include the couch, Marlboro's, Bon-Bon's (do they still make those?), a comfy afghan and the remote control.
Something has kicked the “depression” into gear and it is coming straight for you. Do not sink into a sedentary life style. Do not become idle.
Take a walk, better yet take a run. Go visit friends or family. Go to the zoo. Take a class at the local college.
So much of what your mind is doing is controlled by what your body is doing. I can not stress that enough. It is extremely hard and I feel impossible to get your mind right if you do not have proper diet and exercise. At the very least you will not reach your full potential as a human being if you do not exercise your body and eat right.
You must be active in controlling your mind and not letting your mind control you. You can in fact control what goes into your mind. You can remove the growing negative thoughts and replace them with even more powerful positive thoughts.
But you can not accomplish this if you never leave the couch.