Are you talking about getting certified through AAPC or AHIMA ? If so, yes, they are very difficult, take lots of study and you need a thorough knowledge of anatomy and physiology.
Are you interested in becoming a certified coder? I know you have been looking at billing. Just a thought..every office needs billers. I don't know an office that uses a coder. I am not saying that it is not a good profession but your job opportunities are less, usually with a large clinic or office or a facility.
Recommend you look at codingcertification.org for more information.
Merry