There's a great saying based on airplane travel: In case of emergency, put on your own oxygen mask before helping the person next to you. This little saying sticks in my mind and assists me in separating "self care" behavior from "selfish" behavior -- they are not the same thing.
Selfish would mean, I'm not going to help you -- in this scenario the person on the plane -- at all because I'm too concerned with myself and my own needs.
Self Care means, I will not be able to help you at all unless I provide the safety mechanism for myself first; then my energy will go to helping you.