The sun is currently in a period of low activity but even so large sunspots occasionally appear.
There is a severe shortage of water in this city, so we must give up having a bath occasionally.
Although I broke test tubes and played about with chemicals for fun, I did occasionally manage to obey the teacher's instructions as well; repeating experiments that others had long ago undertaken.
They visited me occasionally.
He occasionally visited me.
Let's occasionally change where we go to eat out.
Teachers should occasionally let their students blow off some steam.