There could be many reasons, one explanation could be that arousal increases norepinephrine and dopamine which can lead to anxiety. So even if jerking off doesn't give you the same energy that a cup of coffee would it can still give you the same anxiety. I definitely have noticed it, if I watch porn for a long time I get jittery.
Also cooming increases prolactin so it takes down the dopamine so you don't stay aroused forever. Prolactin also messes up your androgen receptors for a while. You can even try it out for yourself, try to see how your voice sounds before and after cooming three times. I guarantee your voice sounds a lot weaker after. Its because the androgen receptors have became less sensitive