The Japanese phrase “wasure-mono” translates directly as “forget-thing”, like an umbrella on a train, or a jellied quince in a hotel fridge in Izmir (long story).
I don’t think we have an equivalent phrase in English.
A memento mori encourages us to remember death.
If you absentmindedly forgot death, perhaps just left it behind like a warsure-mono, we could call that obliti mortem:
More experiments with making prints from large, engraved panels of foam insulation. Again with the nasty edges. I’m working on that.
Please excuse the poorly lit photos.