Yes I am asking the same question, I dont know what it means and the manual says nothing about that.
Maybe "during an event" is an alert during high stress episodes (like the other Garmin smartwatches).
And "after an event" is a sort of reminder at the end of the day like "today you had a stressful day". I've seen that there is a feature called "Daily Summary". Maybe stress periods are shown in this "Daily summary".
