Sickle cell anemia is another kind of blood disorder that tends to make the red blood cells change. In this case, although they look larger, they are much thinner and can't carry oxygen very well.
I've always suspected I might have sickle cell trait, which is when you have only one gene for sickle cell anemia.
My father was Lebanese and this genetic trait is more common in Middle Eastern countries, as it can guard against malaria.
Apparently, though, people with sickle cell trait can also have trouble with oxygen flow. I really should get tested at some point.