The antonyms for the term "up surging" that mean a decrease or downturn could be words like declining, plunging, reducing, decreasing, falling, plummeting, descending, sinking, dropping, or slumping. Other words that could be used in contrast to "up surging" include tapering off, shrinking, waning, dwindling, receding, or ebbing. These antonyms suggest a move away from growth or expansion and a shift towards a contraction or a decline. Overall, the antonyms of "up surging" convey a sense of decrease, decline, and falling back rather than growth or advancement.