I used to be this way too. Not wanting to stop the flow of class to ask a question and feeling stupid if I did. Then I started to notice how relieved I was when someone else would do it for me. I was always glad when someone else would ask the question I had been trying to convince myself to ask. It occurred to me that I must not be the only one in the room relieved that the question was asked, but the person asking was the only one with enough guts to actually ask it. After that, I would see it as not only asking the question for myself, but for anyone else who needed it. Now, maybe I was the only one who needed clarifying, and maybe there were people in class who were peeved that I'd halted class, but after a while I just decided they could go to hell.