After a weekend of real sickness (a nasty virus that affected everyone I work and live with), I'm reminded of how illness forms mental states. The strange delirious logic of nausea, the dulled nihilism of stomach pain and the momentary elation that comes from the pain leaving, from health returning.
  I have a friend who has had several bouts of pancreatitis (more painful than child birth, or so he tells most of the women he meets). In hospital, when he needs serious medication, the doctor asks him to rate his pain level. But he cannot remember if this pain is worse than the pain he suffered the last time. We have no memory for pain, no way of judging it in relative terms.
  Every time we get sick we experience it as though we have no basis for the feeling of illness. We might get more used to the processes involved, (I'm a seasoned professional at waiting until I'm in the toilet before I vomit, no matter how suddenly the urge comes upon me.) but the pain, and the essential sick-ness, of sickness is new to us, every time.