Understanding the physiological and emotional impact death has on someone can’t be defined in exact terms. Death happens each and every day and people who experience the loss from a death can struggle with a range of responses. To say that there is a “normal” way to grief would do an injustice to the nature of humankind. It’s no different than staking claim to a “normal” way to express love or stipulating a “normal” way to feel anger. People response differently to emotions based on their own set of experiences and interpretations. Grief, sorrow, or bereavement are no different.
How do we know when to call something “abnormal” if we can’t define what is normal? The short answer is to acquire a sample and evaluate the extremes. For instance, if 100 people who recently experienced loss from death are given a survey and followed up with over the course of a year and 75 of them stated that after a period of one year they no longer struggle with the loss but periodically have feelings of sadness then this sample can be defined as “normal”. Then the other 25 would be the ones that might be considered “abnormal”. This is a very obscure definition of how to define abnormal versus normal. More detail and criteria are examined, so this gives a crude example of scientific justification for normalizing reactions.
That being said, complicated grief can be defined as abnormal grief. The burden of grief is emotionally taxing. Living with grief is a struggle. Those who are unable to process and cope with grief can develop complicated grief. They might find themselves suffering from nightmares and struggle with day to day life. Symptoms of complicated grief might mimic the symptoms of depression. The purpose of identifying complicated grief is to help the individual process their emotions so they can live a more fulfilling life (i.e. shower, participate in social events, eat healthy, find pleasure in day to day activities, etc.).
Working with a therapist, counselor, psychologist or psychiatrist can be beneficial and each individual has the right to decide which professional would best suit their needs. If you are curious about complicated grief, I suggest the following resources (note: the PESI text is the first one I encountered on the topic of complicated grief and I still refer to it today):