Thanks both cougr and Earion! The trouble is with fillers that, if you use them wrongly, so far from sounding idiomatic, they sound unnatural and you stupid.
On the Greek course I am currently studying several of the participants who are assigned to me by the (excellent) teacher monopolise the conversation and, though their Greek is very good, it is laced with too many λοιπόνς and πωπωπωs and other fillers that it sounds ‘overcooked’. I who am naturally reticent, even shy, often can’t get a word in edgeways and when I try to contribute, my mind and words are slow to react and I feel brow-beaten. I am finding this part of the course very difficult.
To try to remedy this, I play in ‘google translate’ what I would like to have said and listen to the voice of the lady who recites clearly but at full speed what I have written and this is helping me to overcome my blatant deficiencies!