sudden and severe
Acute is used in the sentence "Call it acute congestion of the stomach and brain." After reading the sentence, we can easily eliminate the math option "an angle in geometry". Also, the choice "having a sharp point at the end" is not valid. It doesn't make sense to say call it a sharp point congestion. However, the option sudden and severe does make sense. Another contextual clue that validates this answer is in the sentence before that talks about how the fever comes and goes.