Switching from one career to another can be scary, but it also can be a thrilling experience. Look at it as an opportunity to really go after what you want to accomplish in life and make a difference in the world. The key is to take small, conscious steps and prepare yourself for a successful transition.
I worked for Union Pacific. I started out as a conductor at an intermodal switching facility outside of Salt Lake City. We'd pull in trains from all over the country, break them apart, consolidate the freight, and build other trains. It was great until I screwed up and took a management position. Then it became no fun very quickly.