It seems quite appropriate for people who are going through these experiences to feel angry at times. It can even be energising, sometimes, to feel angry.
Where problems arise, however, is if you get "locked into" your anger in a way which makes you unhappy and you can't seem to move through it into some degree of acceptance.
Anger is also a problem when it is expressed in destructive or self-destructive ways - when the feelings of anger and frustration lead to rebellion against diet and fluid restrictions, for example, or to aggressive behaviour towards friends, relatives and staff. When people are angry, they may tend to "push away" the people who want to support them.
Anger expressed in these ways is self-destructive because it puts your health at risk, and - on an emotional level - leaves you feeling even more isolated.
It can feel like the hardest thing in the world to reach out for support when you are feeling angry. Paradoxically, it may be the one thing you can do to regain a real sense of power and control in your life.