'Illness trajectory' or 'course of illness' are phrases that are sometimes used in medicine. They look at time of diagnosis to the time of death. They describe what will usually happen. It is not what will always happen. For some people the time from diagnosis to death is very short. This can occasionally be a matter of weeks. For others, symptoms will slowly become worse over months, even years.
Sometimes with treatment, the progress of your illness will fluctuate. This is often true of cancer. For example, cancer treatments may shrink your tumour. You may then feel well for a while, but your symptoms may return. You may have another cycle of being unwell and more treatment until you are stable again.
Understanding the path or pattern of your illness can help you make important decisions. It may be about your job or any legal matters. It may help with emotional or spiritual issues. You may also want to discuss advance care planning.
You need to understand your illness and your prognosis. This is whether your disease can be cured or only stabilised for periods. You should also be told the goal of any treatment. For example, whether it is to slow progress of your disease, to treat a symptom or help improve your quality of life.
You may want to know exactly what your prognosis is. This is not easy to answer. You are an individual. You will respond differently to a disease or to a treatment than someone else. Doctors will give you an idea based on their experience. They will know what usually happens. An accurate prognosis is not always possible. If the prognosis given is not correct, it can be distressing for you and your family.