old topic, I don't know how I got here, but I want to say something
what you described as a flatline, the sudden loss of libido after stopping pmo, due to the lack of stimulation, sound perfectly normal and makes sense. however, it involves that if you didn't stop pmo, you could go on to being horny forever, which is not the case. at one point, no matter how healthy you are, if you keep jacking off for years, tens of years (do you even realize how much that is?), your body stops responding and shuts down in order for you to recover. a flatline is not necessarily triggered by stopping pmo, but also by desensitization. if the porn you jack off to doesn't deliver anymore, it's like watching cartoons or anything else non-sexual -> no stimulation -> flatline.
those with extended periods of porn use and escalation problems could then end up flatlining during pmo, because the body needs time to rest. hence why I don't think we should get too involved with semantics and definitions, but a working model of the flatline mechanisms.
little trap: if we go into semantics, a flatline is not a loss of libido. abstaining from pmo removes stimulation, hence your brain stops reacting to your urge of watching porn. that urge is not true libido, so the flatline can never be the loss of libido
. it's the loss of the excitement that you used to get before watching porn. since your true libido is inactive (you've been in one for quite a while), it seems like you become asexual for a while. as time passes by, you get your true libido back and that's the end of the flatline.
but I do agree with you, even if some people have low libido for a day, they immediately speak of a flatline, that's not realistic. but then again, our expectations of what it means to be horny are not real either, since we can only compare that with our porn use. porn doesn't resemble reality.