"Fear, I've come to believe, keeps more people from starting businesses than any other single factor. You hear about other obstacles--lack of money, inadequate support, bad advice--but they pale in comparison with the fear most people have that their new venture will fail."
I was in your position two years ago but in my case I had a serious health problem. I was scared shitless. I didn't want to give up my job because I needed the health insurance. But my job was making my health worse. I quit and second guessed myself for a long time afterwards. But two years later I am fighting fit again. Thinking back, my only question is, why did I wait so long to do what was in my best interest? Most people who knew me thought I had the best job in the world. But I was miserable. For several years (!) I listened to them instead of myself and made my health even worse. Complete and utter irrationality combined with a lack of self-confidence. In the end I only did it because I had to, not because I am a shining example of courage. I really thought I was throwing everything away and yet I was so wrong. Let my stupidity be your guide. Oh, and the company went under after I quit. So much for throwing away my security. The question is really much simpler than you think.
-Norm Brodsky http://www.inc.com/magazine/19991001/13574.html