My 24 year old son has achy feeling and pain near rib cage on right side mostly, his ultrasound last week showed slight sludge in gallbladder, howerver,2 days ago after excruciating pain in the ER he had another ultra sound with no sludge, he is getting nucleur gest tomorrow....2 questions, can sludge come and go as one day it showed on one ultra sound a week later it did not show and can this sludge make him feel achy but no fever?