It doesn’t mean “Heaven is in a bad mood”(kivyochol) and now only bad things will happen, c”v. The world is still and always being run buy a loving Hashem. It’s not an especially happy time, we mourn our too-long Golus,etc…..but rest assured Hashem is not “out to get us” in the 9 days.
And you don’t have to mope around or greet everyone with a sad face.