I have been playing trumpet for around 5 years now. At my old high school, I was always 1st chair. I was a decent player aswell. I came over to my new school and everything is fine. The trumpet players here are no lifes (their entire life is devoted to trumpet, I don't mean as in playing for a living, I mean as in spending 8+ hours a day every day playing trumpet..) so I'm third chair now... Anyways I am leader of the third chairs and I was getting along fine until November. We had a 4 day weekend, I come back and my trumpet isn't sounding right. I try to play a 3rd space c and a high e comes out. I try playing a low c and a low f comes out... I can play a g just fine but when I try to play a c it skips straight to the high E... I thought this was my trumpet at first, but I've been playing other people's trumpets and I have the same problem on theirs. Today in class I had trouble keeping up on the lip slurs. THE LIP SLURS... I have no idea what's changed... I have tried using faster air, that just makes it sound more retarded. I know its my embouchure but I don't know what's changed about it. I can't just go up to our instructor and be like, "Hey I just happened to forget how to play an instrument I've been playing for 5 YEARS" I'm seriously considering dropping band because of this, I had better tone quality in the 6th grade... (I'm in 10th) My embouchure was just fine before... My beautiful embouchure... years of technique lost... I don't know what happened over that weekend, I've gone summers without practicing and still been fine. As a result of all this, I have much lower self-confidence in my playing, if the music says ff, I'll play ppp so that nobody hears me fail. Oh and btw on an off-topic note, I've never been a die-hard fan of playing trumpet. It's a limited instrument, and note quality depends heavily on the user's trumpet quality (mine sucks) and the lessons taken (If you haven't figured it out by now, if I can't afford a new trumpet I can't afford lessons either) I've always wanted to play percussion or alto sax, but my first band instructor said STFU and CHOOSE BETWEEN FRENCH HORN AND TRUMPET. I decided on the trumpet... Then again, I don't dislike playing it either. It's brass, and I like playing brass..
EDIT: Also every day I have to tune my trumpet differently, apparently I sound different every day. And I don't mean slight tuning, I mean like at least a good half inch or more of adjustment on the tuning valve.