Tiki doing worse after prednisone and de-wormer

Tiki is a 9 yr old male indoor cat.  He started developing a cough that sounded similar to a hairball but wet instead of dry.  This was his only symptom.  I took him to the vet 5 days ago, they did a chest x-ray (negative for pneumonia or tumor, might be asthma or lungworms).  They also did blood tests, elevated white cells, negative FIV, negative heart worm, otherwise normal.  They thought it might be asthma or lungworm so they put him on prednisone and a de-wormer (begins with an F but cant remember the name).  Now its been 5 days, havent heard him cough at all, but now he is acting like a sick cat.  Malaise, not eating or drinking much, appears to have lost a decent amount of weight.  He always follows me around and is looking for attention and now just lays in the corner or under the bed.  Is this just side effects of the meds?  or should I be worried?  Should I stop the meds and see if he feels better?

I don't know about the dewormer but these aren't normal symptoms with the pred.  Pred will usually increase appetite and activity level.  Have you called the vet's office and told them about the symptoms.