A Clear can still get sick, but this occurs far less frequently than before he became Clear. In other words, a Clear still has a body and bodies are susceptible to various illnesses. However, no longer having their reactive mind, they are much more at cause and are not adversely affected by many of the things that would have caused psychosomatic illnesses before they went Clear.
To measure a Clear only by his health, however, would be a mistake because this state has to do with the individual as a spirit, not as a body.