Prototype can be as small as Wireframes, Product Specs, HTML mockups. You dont need to change/leave your job to do that.

If you have been living with the idea for few weeks/months are also very passionate about it. Three four nights or weekends are sufficient to start with the sketches and wireframes.

Once you have it ready, show it to few friends, industry experts you know and iterate until you will confident to take the next plunge. Because after that there is no going back.