I'm dense, but I've only noticed now that when I equip the glowing amulet my maximum sanity goes down 20 points. Like, my sanity was 95/100, but then I equipped the amulet to go underground and suddenly my sanity was 95/80 and then soon after 80/80. I couldn't find any info on this either in the guide or in the update notes, so is this working as intended?