If I'm sick, I listen to my body and take care of myself. depends on the severity of the illness.
However, if it's TOM, I'll do my regular routine. Life doesn't stop for a woman when Aunty Flo comes a visiting. I've got stuff I need to do. I can't lie in bed waiting for my menstrual cycle to pass. wouldn't that be great ? ain't happening. gotta get moving.
Now, there are women who do have really painful menstrual cycles that can side line them. If you are one of those women, that's something you must discuss with your doctor. There are medications (or even birth control) that can help regulate your period so that they aren't so difficult.