Hi, SHARON . . . You do not necessarily have to bump your hand to get a bruise on the back of it. I remember once dropping something down between the driver seat and passenger seat of our truck. I had to squeeze my hand down into a tight area to retrieve it and later saw that the hand was bruised.
It took about a week for it to be mostly gone if I remember right. I think hand and foot bruises look more intense most of the time than bruises elsewhere because the veins are right there between the skin and the muscles (not as much fatty tissue to help hide them).