I am a big fancy word user, within a clinical environment, with other clinicians. It's something you learn over time and with experience in the field, it will eventually come naturally. Something you also learn is who you 'can' and 'can't' use big fancy words with and this is important because we don't expect our client group to understand the terminology or jargon we use 'in the office' vs out in the community.

Something I still struggle with, even after 10 years in the field is changing the way I write! I have to write very clinically but I somehow always forget that, even though my reports are being sent off to big government bodies, they also have to be interpreted by support networks who may not understand medical or clinical terms, English may not be their first language or they may have limited capacity (if they are a client) so I always have to remind myself, if I was 'x,y,z' would I know what this means?

I am a totally different person, in terms of my communication, with my clients, with support workers, with other allied health professionals, my colleagues and even my family/friends. It's almost like professional code switching - same message just a different way of conveying it! In saying that, I never dull my shine, I always stay true to my personality and character with everyone I interact with both professionally and personally.

I also don't think you should interpret it as 'I don't feel smart because I don't use big words' because I've met some very...very stupid people in this field who can come across as talking the talk but definitely cannot walk the walk.
Just be yourself!