.....excessive use of caffeine (and i would suspect that "excessive" is user dependent) is a known cause of rebounds.....
.....inconsistent use is a known cause of headache (that i know not the proper term for)....consider the well reported "weekend headache" where the worker drone abstains or greatly reduces typical weekday consumption...and the body cries out and objects to lack of the normal with a "reminder" headache....
....personal....anecdotal...talkin about me.....over years of dancing with the devil practice.....I found that abstaining from caffeine at ALL times, other than when hit, resulted in fewer hits and improved efficacy when used FOR a hit. the body is a marvel at maintaining stasis...it'll get used to and regulate for all kinds of differing factors. if one regularly ingests caffeine there becomes an amount that is "normal" and effects are dampened.....abstaining and then introducing a large bolus of caffeine as an abortive at least temporarily overwhelms the dampening effect, and the desired vasoconstriction aids in CH suppression (always hit the O2 concurrently, if possible). works for me.....YMMV
....triple strength, HOT coffee used to be my go to...a little inconvenient and hard to get down but effective. energy drinks, kept really cold and pounded FAST became an effective replacement, i think the additional ingredients (taurine, et al?) improved effect...but DAYUM what an awful taste, and SO MUCH sugar or the dreaded trigger, aspartame. the 2 oz 5-hr energy types became my go to.....LOTS of caffeine+, minimal sugar, and easily carried everywhere............
best
jonathan