This does not happen often. I can't remember the circumstances around when it did (not recently) happen; I play high B or higher, got an instant headache, tense my abdominal muscles; it was gone like that.
Must clear up some things:
-the headaches would last 2-5 seconds after I stopped, but clear up instantly after I stopped and tensed my abdominal muscles
-bending my knees slightly seemed to help in that range, but I get a weird feeling in my midsection like stretching a cold muscle if I held the note long, i.e. 5 s or more (like I said, hasn't happened recently)
-the headaches happen after I stop,as if all is fine while going out (cracked note or not) but it blows up after I stop and I get the headaches
-I don't take "chest-breaths," I breathe "naturally" (stomach goes out)
-I always keep air moving in or out; I don't like to hold it then play
-my lips never hurt from pressure, but I may crack (or buzz becomes whooshing air) @high C or higher after long play/practice time
-this has only happened when I practiced at home, but not for a month now
-I've been working on high C to at least D for a few months (long tones high A-high D; arpeggios for Bb, B, C, and D scales)
My music instructor will connect me with a trumpet instructor soon.