Giving first priority to myself is not a selfish behaviour.

Selfishness has a fairly precise meaning: taking more than your share, at someone else's expense. Almost nothing on a normal person's list qualifies. Sleeping enough. Eating lunch sitting down. Keeping the physio appointment instead of driving someone to the airport for the third time this month.

The people who worry hardest about being selfish are, reliably, the ones already running a deficit. Put yourself first for one thing today, something about the size of an hour, and notice how little actually collapses in your absence.