A patient with sickle cell crisis will most likely complain of severe pain.
A patient with sickle cell disease have an abnormal amino acid composition of hemoglobin, leading to a comformational change to insoluble proteins whenever the red blood cell is deoxygenated; this leads to a change in shape from biconcave to sickle shaped. In sickle cell crisis, the abnormal RBC clump together (easily, because of their shape) then obstruct small blood vessels in the extremities and other organs, causing severe pain.