I forgot to add an explanation for the second part of your query..
پیش لفظ is the usual construction for the English "foreword" but پس و پیش لفط means something different I believe.
پَس means "after" and پیش means "before".
So, in toto, the meaning could be...
We were dozing off after and before speaking...... or in another words....We were dozing off during the conversation.
Let's see if other friends have a more reasonable explanation.
Edit. پس و پیش کرنا means " To shuffle, prevaricate, boggle; to hesitate, demur, doubt. "