Many of us see the immediate physical effect of relaxing, being happy, and smiling. That alone can erase so much of the stress and unhappiness that causes people to look, well, stressed and unhappy.
Two days for actual physical changes that you'd notice - like in terms of eyes looking wider, boobs growing? I doubt it, although it took about one week on low dose HRT for my boobs to start hurting and feeling hard under the nipple. I guess it wouldn't be impossible for changes to have occurred very quickly for you if you're on regular dose.