I went through this phase recently. And there was a surprisingly easy solution out of it. Finding new clients and get into a habit of working out. Both these activities have given me a new lease of energy to approach problems. As the clients have right to fire you, you have the rights to fire the client as well. We all want to be nice to our clients but sometimes our decency is mistaken for gullibility and they tend to take advantage of these situations. Working out releases the necessary endorphins to combat the depression. Just a 30 minute jog everyday can make a world of a difference to your life.