I can't say I understand the feeling as I haven't been yet battered by the corporate machine.

My advice is to try and find something you can do by yourself that you will enjoy. Obviously, it would be better/more profitable to stay within your field, but who knows - lots of successful people change from field to field and remain successful (see James Altucher who has had many career changes). I would suggest you put some serious thought into what this special thing is, though. Do not quit your job before you do.

Some people might tell you to quit immediately for your own health, but I think putting some serious thought into your options will go a long way into keeping you happy. Sure, you're working in some corporate gig, but you've got some consulting business you're planning...something like that. Good luck, whatever you decide.