It was like a ton of bricks was lifted from my shoulders

This mash up involves the idioms “hit like a ton of bricks” (surprise or shock) and “weight was lifted from my shoulders” (relieved of a responsibility), both referring to weight, but one indicates weight off and the other on.   The speaker appears to be thinking the word “weight” but somehow “ton of bricks” replaces that thought and the malaphor is born.