I try to shift what I concentrate on to something a bit in the future. Think about what they are going to discuss in class and what you would like to learn about it and/or how much of a pain it might be to find and get notes from someone to copy, etc. if you miss this session but move away from the immediate, personal failings, and other people thoughts. If I have to, I think about what I am going to do when I get home, or something I am looking forward to later in the week, etc., I try to create a "bridge" from here to beyond whatever is difficult for me so it is put more in perspective instead of being so big, front and center.

Keep reminding yourself of your current "problem" (have to get to class) and ditch all thoughts that don't help you figure out how to do that (Maybe you are/are not "lame," so? How does that help anything? It's just a distraction.). If you are attacking yourself with lame words then get angry at the attacking part of you and "correct" it/make fun of it. "I may be 'unconvincingly feeble' (definition of 'lame' :-) but I certainly have nothing wrong with my feet or legs and I want to get to that class and will walk there if I have to; YOU stay out of this!"