To me:
'Bad case of (an ailment)'
sounds anything and everything that is either the direct result of an ailment; for example:
I have a bad case of the flu.
would cover other symptoms that might accompany it in a given case (i.e, headache, sore throat, body aches, etc.) Is that right?
Whereas if I said:
I am trying to get over the flu.
means I am doing my best to recover from it. Correct?