Definition: Homeostasis is the process by which the body attempts to maintain a state of stable physiological balance. The body needs to maintain homeostasis in order to stay alive. If you take a psychoactive drug, your body may attempt to bring itself back into this physiologic balance, and this may create a rebound effect.
If you get too cold, your body will maintain homeostasis by causing shivering, which will warm you up. If you take a drug sedative drug, the body may attempt to maintain homeostasis resulting in agitation.