I have this right now and feel very similarly. For me it's a case of not knowing why I do what I do, not clearly identifying what it is I actually do for my clients/employers, and what in the world I am capable and willing to change. It's also wintertime, which doesn't help.

Possible cause: I've been listening to a lot of business podcasts lately (at least 2 hours worth a day) and I've found myself comparing myself to other people who are more successful than me. I realize (from listening to podcasts) that this is a bad thing to do and I realize that success is relative, but it's still happening.

I tried chilling out on purpose. In other words, I purposefully started playing. I chose to start playing Minecraft with my kids. I also joined the YMCA and started going swimming there after work. Finally, I have cut down on the number of podcasts I listen to and started listening to music (on CD). I do not listen to the news as it gets me down.