1. and work up a sweat Lit. to work very hard and sweat very much. (In the way that a horse works up a lather.) Don't work yourself up into a lather. We don't need to finish this today. I worked myself into a sweat getting this stuff ready.

2. . Fig. to get excited or angry. (An elaboration of work oneself up to something.) Now, now, don't work yourself up into a lather. He had worked himself into such a sweat, I was afraid he would have a stroke.