A slight rise isn't 'plummeting' in anyone's version of English. It has been soaring for a long time. But who cares about silly semantics, other than you?
Those two concepts are not antonyms, nor even related.
Somethings can be unrelated or related, and also not mutually exclusive (i.e. can exist at the same time), and mutually exclusive.
For instance, it can be raining and sunny at the same time. Just as it can be not raining and not sunny at the same time. Or raining and a Tuesday at the same time.
There are so may examples of some things not being related, and not being mutually exclusive that it is impossible to present a fraction of the examples.