Gestaltzerfall; shape decomposition
Psychological phenomenon where prolonged staring or repetition causes a familiar shape or character to lose its meaning and appear as a collection of meaningless parts. Often used colloquially for kanji that suddenly look strange.
When you write the same kanji over and over, you can experience Gestaltzerfall and suddenly not know whether the character is correct.
Gestaltzerfall is a psychological term for the phenomenon where the overall coherence of a shape is lost.
From German 'Gestaltzerfall', literally 'shape decomposition'. The term was introduced into Japanese psychology and later popularized online to describe the experience of kanji or familiar patterns suddenly looking unfamiliar.