I'm having the same problem with Opera lagging a lot, since 2 or 3 days ago. But in my case I really don't know why this is happening, I had no hardware alterations and the tabs I've got open are the same I usually have on Opera. Nothing different.
Still, Opera keeps lagging and sometimes freezing as you mentioned. I updated Opera today hoping the situation would be solved, but unfortunately it didn't.
All my other browsers are working without any issues.