Your bone marrow creates new cells that become your red blood cells, white blood cells, and platelets. When you have aplastic anemia, your bone marrow slows or stops making these cells. It causes your blood counts to be low across the board. It makes life more difficult because you could have bleeding problems with low platelets, or be more prone to sickness with low white blood counts. The low red blood count affects how much oxygen is in your system, and you can become dizzy or have trouble breathing.