I once quit school for a few months (although it was not really with approval of my parents). I basically just stayed home and there was not much my parents could do about it. This had been going on for a few years.

Eventually I got tired of doing nothing with my life and promised myself I would do better in the next year. What really helped me was exercising. I would spend at least an hour every day (light) training to get into shape. It gave me more energy and it's also actually somewhat addictive and enjoyable once you get into a proper routine. If you are able to do so I would suggest doing it outdoors or in a gym, but at home is fine too (I had a training bike in a room with a TV, and synchronized my training with my favorite TV shows). Also, don't give up if you miss training, it won't undo any training you do afterwards.

As for the mental aspect of it, can't say much other than that depression is usually temporary (even though it might not seem that way), and even though life might suck, doing something is still more fun than just staying home all day.