Alcestis, your story lines up perfectly with the Jungian hero's journey, how you arced into the underworld and back again. Are you an example of feminine-energied representation, a yin hero rather than a yang hero? A yang hero hurls him/herself actively to die in another's place, a theme that familiarly sends young men to wars and wars. The yin hero instead quietly passes away for another, and the theme is less acceptable for some reason.
Alcestis, what are you trying to tell us?
Are you just a better person or a doormat? You trying to make martyrs look bad? You just lording it over us? I hear you saying something else, which sounds like this: What if we have a great power to save someone else, and we use it consciously instead of unconsciously?
What if we awaken to our heroic power and to its proper use rather than letting it use us? Instead of busily giving our lives to every person whether they ask or not, what if we resist our instinct to give our lives up before breakfast every day? What if we reserve this supernatural ability to make a deal with Thanatos until one is actually on the table? And then freely given, however our gift is used, we wait only for the right time to give it again.