Susan Anderson (psychotherapist)
While Kübler-Ross, Anderson, and others have attempted to define discrete stages of grief, such as an initial period of numbness leading to depression and finally to reorganization and recovery, most modern grief specialists recognize the variations and fluidity of grief experiences, that differ considerably in intensity and length among cultural groups and from person to person. No grief stage theory has been able to account for how people cope with loss, why they experience varying degrees and types of distress at different times, and how or when they adjust to a life without their loved one over time.
Ambiguous loss
The difference between regular grief and grief from an ambiguous loss is the type of loss creates the type of grief experienced. Grief in ambiguous loss can be both beneficial and difficult. Since the grief in an ambiguous loss differs than the linear stages of grief there is no pressure to move on or achieve closure, and this allows for people to remember the lost loved one and move on with relationships and life. There are three specific types of grief that can develop from the type of ambiguous loss. 
Anticipatory grief occurs before bereavement, mourning after death occurs, and upon realizing that death may be imminent for a loved one, anticipatory grief sets in. This type of grief is common among families who have a loved one living with Alzheimer's disease. The grief becomes anticipatory due to the knowledge that the loved one's mental state will only become worse, so the grieving process can start very early.