I can't quite get my head around the difference between misapprehension and its opposite apprehension.
I understand the latter, but the former still eludes me.
Apprehension is not usually used as the opposite of misapprehension.
Misapprehension is another word for misunderstanding - "A mistaken belief about or interpretation of something".
Apprehension can mean "understanding", but is usually used to refer to a feeling of fear or misgiving about a future event.
"Misapprehension" only negates one meaning of "apprehension":
misapprehension — a mistaken belief about or interpretation of something
apprehension — understanding; grasp
The other meanings of apprehension are generally not relevant to the meaning of misapprehension.
Usage examples from the same dictionary I grabbed the definitions:
the pure apprehension of the work of art
she must have been laboring under the misapprehension that you are nice
So, the way I take it is that misapprehension is that you are worried about something for no real reason. So if apprehension is to be worried about something before it happens the misapprehension is to be worried in advance about something that is actually not something to be worried about?