Really can't explain it. Had a semi-consistent High C two weeks ago, and now I cant tongue a D in the staff without airy crapness. I have given myself rest, I have done lip slurs, I have intelligently practiced for hours on end. I am just off. My lips are just off. This has happened before, but never to the extent where anything above the staff is absolutely unattainable. I have Honors Band material to study, and all I have been doing the past weeks is strained lip slurs up to E in the Staff. My tone is great where I feel comfortable, but my range limits me to books instructors assign their students the first year they begin playing. Any advice would be helpful. Merry Christmas! Edit: My endurance is absolutely garbage. I can play the first two and a half studies of the Arban's First Studies before I falter. I will work on my getting my trumpet playing up to speed, but is there anything I can do to improve my trumpet playing without actually playing it. I am sight-singing when I cannot play any more.