"Client" was new to me, too, and completely foreign. I do not associate anything negative with the term "patient," but others probably do. It was explained to me that "client" connotates the ability to pick and choose which health care facility to utilize. To me, a patient does that, too, but for those in administration or in the business side of health care, patients are customers/clients. In day to day care, I use the term patient, not client or customer; so do my co-workers.