Could it be that the ebbing and flowing of the introvert and extravert’s so-called energies, the one’s need to resource in private silence and the other’s excitement at digging into a crowd of strangers, are the flip-side of their anxiety? The introvert loves to be alone, to wander through es thoughts and inner life, calming eself so far down that minute feelings and emotions begin to appear in their minuscule glory; however, e has little practice at groups, cannot solve the three-body-problem of social interaction, and quickly paniks in complicated social settings, es mind running in circles not figuring out how to behave, repeatedly stumbling down social dead-ends, which in turn generates negative emotions, anxiety and stress, causing his mind to stall and go blank. The extravert must live in groups, having always been more comfortable interacting with others, deciding together, erecting friendships and leaning on them at all times; as soon as e is alone, however, e paniks, too, for suddenly there is no one to ask or interact with, and es mind begins to spin on nothing, the constant influx of activity and communication having suddenly stopped, resulting in a loneliness and boredom that e has no practice dealing with and truly fears, which in turn oozes into sad and tiresome feelings, anxiety, stress and once more, a stalled mind.
So it would be anxiety that saps one’s energies, and the mere lack of it would correspond to the positive energies of one’s normal, habitual settings. So the introvert does not build up “energy” when alone, only to spend it at parties, but instead builds up negative emotions at parties, and falls back on es comfortable routine when alone. If such is the case, we can learn to not “lose energy” in “bad” situations, but instead learn to watch and counter the negative emotions as they arise.
This might be a mere question of metaphor, how the assumptions behind our pictures compell us to act in certain perhaps unecessary ways. The energy metaphor assumes a fixed resource or repository which is inexorably depleted until replenished; it tells us we cannot change how our energies are spent, only when. The anxiety explanation, on the contrary, does not posit a positive and scarce constant of energy but rather a source of negative emotions, which, as many such states of the mind, can probably be controlled and mastered.