I would reset the tension back to what it was to start.
Then I would indeed clean out the bobbin area. I've been amazed how many times when something just started going not right was solved by doing that.
And I would put on a new needle. I buy my needles in bulk and on sale and figure they are cheap compared to my time and my fabric. Even a brand new needle can have a slight manufacturing defect.
So with an overall cleaning and new needle and rethreading -- solves most but not all "it was ok the day before" issues. But we are here if it doesn't!