Every time you die in Dark Souls 2, your maximum HP decreases slightly, and it continues to decrease more and more after each death until your maximum HP is reduced to about 50% of its normal value. In addition, your character model becomes more and more decrepit ("Hollowed") as this penalty increases.
I was under the impression that by burning a Human Effigy at a bonfire (to "reverse Hollowing"), you would return to human form and regain your full HP pool. However, I burned a Human Effigy at a bonfire (specifically, the first one in The Lost Bastille), and I received a message that I was now protected against foreign invaders, but my maximum HP didn't change at all, and my character still looks as Hollowed as ever. It also meant that I had essentially wasted an Effigy, which I wasn't pleased about.
Is there something I'm doing wrong, or a faulty assumption I've made about how this works? What do I need to do to restore my HP pool?