Once you get below 5-7 mg of daily - it varies for people - your adrenal function needs to start to kick back so that you get the correct amount of cortisol for daily needs. That is, the reduced prednisone dose is no longer supplying all the cortisol you need for your energy needs. After an extended period of steroid use, the adrenals can be slow to wake up and some adrenal insufficiency can occur until it all becomes balanced again. The length of time this takes varies for each person.