and I would have to concur with your thought on that -(not only from my own first hand experiences)
but also when I think about anything in life-
it all happens in phases.... everything, the seasons, the way we learn or age or heal physically, or love, all of it, it's all in phases.
So...I think you stumbled onto something critically important there with your premise on "phases".
And that "selflessness" is most assuredly a very heady feeling too (even addictive perhaps, I would say) and there's something so paradoxical about it too- in that by losing the self in the task or your commitment to the task, one seems to gain such a sense of....of what would you call it?.....accomplishment? Giving? Groundedness (is that a real word?) or connectedness?
Now me... I get my doses of "selflessness" from volunteer work - but I believe it would be sorely lacking in the huge adrenalin push you'd become accustomed to-
Just one last thought and that is that sometimes- the "phases" have their own time sequence and you can't force them, but just have to "let it happen".