Not a dumb question. Important question.
I think in pictures, not words. When I read, or talk/communicate, I am translating in my head the visual of what that word means.
For example, when I read the word 'running' in my mind I'm picturing someone running so that I can relate to the word. I think in ASL not English.
I actually posted a thread about this last year and Jillio provided an excellent, how do you say, explanation?
http://www.alldeaf.com/our-world-our-culture/85467-its-up-debate.html