By definition patients are dependent and non-autonomous. Quite different from a client or customer. More akin to a slave, I am sorry to say,--as perceived by the non-dominant participant in the relationship. They routinely understand that their very lives depend upon keeping the master professional happy. To be labeled a "bad patient" can result in death.
In my extensive career, I have never heard of a person referring to themselves as a patient, except when deferring to the power of a professional. It is not a term that many choose for themselves.