Funny you should say that. Fifty years ago we were warned that "paciente" only had the meaning you mentioned, and never referred to physicians' clients at all! Instead, the preferred word was "enfermo." However, as soon as I got my MD in '76 and started interviewing lots of Spanish speakers, I immediately noticed the "forbidden" usage everywhere. Perhaps the change began as more Spanglish sullying my Castellano; but it also reflects a gradual realization in society, no matter which language you use, that you don't have to be sick to need health care.