Present reasonable evidence to Court that the condition mentioned in the certificate is untrue. Example: Doctor’s opinion is that the patient is unable to move around as usual and needs bed rest, but patient is seeing doing all routine activities like going to market, movies, travelling, etc. Other point could be patient was not in town in the period during which certificate mentions the patient to have visited the doctor.
Exact content of certificate needs to be read.
Also, how significant the certificate is to the case needs to be looked at. Many times litigants simply take certificate for deferring the case and getting a new date for hearing.