How do you pick up where it was left off?

Let's say you had a very good ongoing chat for a couple of days.
Then there was a 2 days slow motion when only couple of very short messages exchanged. (weekend)

How do you pick up from there? Like if you miss that earlier conversation but don't know how to continue or restart?
You don't really know what the other person thinks.
Is it possible to continue or is it unusual?