@perfectjob This job sounds great; good for you! I have felt many times what you have felt...and some people close to me have wondered if maybe in my case it was some sort of mild depression. Have you considered speaking with a professional? I should emphasize that this might not be any sort of mild depression but the "American way", as others have eluded, where reaching a partocular level makes one feel like it might noe be "enough" (whatever that means).
By the way, may i ask if you wouldn't mind sharing a bit more what your job entails? I'm a little older, and admittedly at a different stage of life, but your role sounds like what i might like...maybe, depending on what you actually do for your living. If you don't want to share here, feel free to email me privately. (My address can be obtained by viewing my HN profile.) Thanks, and I hope that you feel better! As others tell me: life isn't as bad or as boring or as unfulfilling as you might think! :-)