Homeostasis refers generally to a static state of the body's physiological systems. The body has so many different types of systems that it may be homeostatic in some regards and off balance in others. Generally, homeostasis and disease are inversely related. When the body is fighting disease, it is usually out of balance. There do exist situations in which the body may be in balance and still have a disease, though this is usually reserved for cases of chronic disease.
Disease can be thought of as an irregularity of the body that poses a threat for harm. It comes in many forms — sometimes pathogens like viruses or bacteria cause disease, while other times genetics are to blame. There are instances in which disease can be rather ephemeral and other hopeless cases of diseases that may last a lifetime. Thankfully, modern medicine has come up with many ways to combat disease, although there are still many medical limitations.
The term homeostasis can be broken down into roots for better understanding. Homeo means similar and stasis, a derivative of static, refers to the act of standing still. Put together in terms of the body, this word describes a steady rhythm of orderly function. Steady state, which is similar and often confused with homeostasis, is different.
Steady state refers to a controlled, static state, but it is elevated above the norm. An example of this would be a long-distance runner settling into a training jog. After the initial increase in cardiovascular function is accounted for, it remains steady for a long period of time while the run continues.
Disease requires immediate action of the body to prevent harm. Homeostasis and disease are not friends — they do not like each other. The body needs to act quickly to fight the causes and effects of disease, and this requires a boost in many systems. Sometimes, this boost may be cardiovascular, but other times, different somatic systems may be called to the plate.
The exception to this rule is in the case of chronic disease. Many chronic diseases, such as diabetes, take place over long periods of time. They may be dormant, sometimes showing little harm, or very active and life threatening during other phases. When dormant, homeostasis and disease can actually coexist, surprisingly. When active, however, it is back to usual for homeostasis and disease, avoiding each other at all costs like the enemies they were meant to be.