Generally speaking people who feel this way are trapped into only thinking about (now). This keeps them from having long-term view perspective about life.
Hypothetically imagine a 7 year old boy who is bullied by a 9 year old boy. Every time he sees the older child his heart races, he shakes, and fights the urge to pee on himself. In his (limited) view of life he can't imagine some day graduating from high school, going to college, falling in love, finding a good job, starting a business, having a family of his own, and traveling around the world. The only thing he can think about or imagine is what it's going to feel like if this 9 year old catches him and punches him in the face!
Depression is all about "short-term thinking". It's imagining that tomorrow is going to be just like today! Whenever people (allow) themselves to have such a narrow view of life it intensifies their depression. Some reach a point of feeling there is no reason to go on living.
The first thing I do when I'm blindsided by a disappointment of some kind is I tell myself; "A year from now you'll be laughing at this."
This accomplishes two things immediately. The first thing is it forces me keep things in perspective. Whatever I may be going through or feeling is in fact (temporary).
Secondly it takes me mentally to thoughts of a "future tense" scenario where I'm on the other side of the issue sharing my experience with friends and family laughing about how I felt at that moment. Success often has a way of making past struggles humorous.
The next thing I do is try to find some quiet time and think about all my available options. This may take a few days or a week to sort out but eventually "instinct" or some sort serendipity or "aha" moment kicks in. This may happen while walking/exercising..etc
The only actual cure I've found for depression is taking action. Simply focus on what you (can do) today and gradually step by step things get better. Another "trick" I use is I always have (something) on my calendar to "look forward to". It doesn't have to be a "major event" just as long as it's something (you) want to see or witness. It may even have to do with your child's activity, an upcoming movie, anniversary, party, vacation destination, a play, concert, reunion, or holiday festivities.
One of the reasons people stay depressed for long periods is because they don't have anything to "look forward to".
Life is a personal journey. Enjoy the highs and learn from the lows.
One man's opinion! :-)