My wife has GBM. They use the corticosteroids to fight inflammation and suppress your immune system. The steroids manufacture cortisol. This rush is the extra cortisol the steroids are manufacturing. It takes some time usually a coupe of weeks for your body to adjust. What will happen is your body will shutdown production of cortisol because it no longer needs it. The cortisol rush can cause other issues. Lack of sleep, Moon face, increased blood sugar. Its not a good thing. In addition , once your body has stopped producing cortisol you taper very slowly to get off the steroids. To quickly and your body will have increased pain and discomfort. So while good up front its not your friend. Google corticosteroids and cortisol. Lots of information.