I don’t think it’s blanket immunity. He can’t be sued for anything he says on the House Floor or in Committee. He can however be beaten with a cane.
In the words of W. C. Bryant, "Has it come to this, that we must speak with bated breath in the presence of our Southern masters?... Are we to be chastised as they chastise their slaves? Are we too, slaves, slaves for life, a target for their brutal blows, when we do not comport ourselves to please them?"