They have a name for it
Semantic satiation (also semantic saturation) is a cognitive neuroscience phenomenon in which repetition causes a word or phrase to temporarily lose meaning for the listener, who can only process the speech as repeated meaningless sounds.
Actually, a whole lot of terms. Who knew?
“Many other names have been used for what appears to be essentially the same process: inhibition (Herbert, 1824, in Boring, 1950), refractory phase and mental fatigue (Dodge, 1917; 1926a), lapse of meaning (Bassett and Warne, 1919), work decrement (Robinson and Bills, 1926), cortical inhibition (Pavlov, 192?), adaptation (Gibson, 1937), extinction (Hilgard and Marquis, 1940), satiation (Kohler and Wallach, 1940), reactive inhibition (Hull, 19113 [sic]), stimulus satiation (Glanzer, 1953), reminiscence (Eysenck, 1956), verbal satiation (Smith and Raygor, 1956), and verbal transformation (Warren, 1961b).” (From Leon Jakobovits James, 1962)