Can selfishness be healthy if it means taking rational care of your life?
Yes, if selfishness means rational self-interest, not impulsiveness or exploitation. Taking your life seriously includes caring for your body, protecting your attention, choosing relationships well, and refusing patterns that predictably damage you.
This is different from "I want it, so I should have it.". Rational self-interest asks whether the choice actually serves your life in context. Sleep can be selfish. Training can be selfish. Saying no can be selfish. So can rest, pleasure, work, study, and friendship.
Objectivist ethics treats a person's own life as the proper standard of value, requiring rationality, honesty, integrity, productiveness, independence, pride, and justice. In practice, healthy selfishness is not indulgence. It is stewardship.