sweat blood

1. Also, sweat one's guts out . Work diligently or strenuously, as in The men were sweating blood to finish the roof before the storm hit . The phrase using guts was first used about 1890, and that with blood shortly thereafter.

2. Suffer mental anguish, worry intensely, as in Waiting for the test results, I was sweating blood . This usage was first recorded in a work by D.H. Lawrence in 1924. Both usages are colloquial, and allude to the agony of Jesus in Gethsemane (Luke 22:44): “And being in an agony he prayed more earnestly: and his sweat was as it were great drops of blood falling down to the ground.”