I am not the most regular player on Subeta. Mostly my professional life keeps me busy.
I haven't changed my avatar in forever. I was shocked to find out that I am no longer a zombie. I never took a cure or a potion.
I simply seem to have stopped being a zombie. Was there a reset?
Whenever you please. It's a skin. Go into your wardrobe and select the skins tab, then click clear current skin. You'll still have your zombie skin if you ever want to return to the undead. c:

if you never personally cured or removed your zombie skin, it's possible it got reset at some point due to some sort of wardrobe/HA bug. depending on when this happened, the zombie skin may or may not be available in the skins tab of your wardrobe. if it's not, that probably means you got "cured" before zombie skins became unlockable like they are now. unfortunately in this case, i think the only thing you can do to get the skin back is wait for survival (in february) and get re-infected with the virus you had.
What type of zombie were you? You might still technically be a zombie. I came back from a 7 year hiatus, during which time they overhauled the wardrobe and made the skins system. My “skins” before hiatus were layered: I was an unhealed Eyesore zombie, with the Deer zapper skin on top. On >this page here< you’ll see the counts of people left with actual zombie viruses, I’m that 1 Eyesore zombie even though it doesn’t show on my HA!