When a person loses someone close to them, it is natural to grieve. This process takes time and usually includes many different emotions and behaviors. People with cancer and their families may also grieve other cancer-related losses. These may include the loss of a breast, the loss of fertility, or the loss of independence.
The terms “grief,” “mourning,” and “bereavement” have slightly different meanings:
Grief is a person’s emotional response to the experience of loss.
Mourning is the outward expression of that grief, including cultural and religious customs surrounding death. It is also the process of adapting to life after a loss.
Bereavement is the period of grief and mourning after a loss.
Common grief reactions
Reactions to loss, called grief reactions, vary widely from person to person and within the same person over time. Common grief reactions include difficult feelings, thoughts, physical sensations, and behaviors.
Feelings. People who have experienced loss may have a range of feelings. This could include shock, numbness, sadness, denial, despair, anxiety, anger, guilt, loneliness, depression, helplessness, relief, and yearning. A grieving person may start crying after hearing a song or comment that makes them think of the person who has died. Or that person may cry for no reason.
Thoughts. Common thought patterns include disbelief, confusion, difficulty concentrating, preoccupation, and hallucinations.
Physical sensations. Grief can cause physical sensations, such as tightness or heaviness in the chest or throat, nausea or an upset stomach, dizziness, headaches, physical numbness, muscle weakness or tension, and fatigue. It may also make you vulnerable to illness.
Behaviors. When a person is grieving, he or she may struggle to fall asleep or stay asleep. He or she may also lose energy for enjoyable activities or lose interest in eating or interacting socially. A grieving person may also become more irritable or aggressive. Other common behaviors include restlessness and excessive activity.
Religion and spirituality
Grief and loss may also cause a person to question his or her faith or view of the world. Or it may strengthen the person’s faith by providing a new understanding of the meaning of life.
Each person experiences grief differently. Often, a person feels grief in waves or cycles, with periods of intense and painful feelings that come and go. People who are grieving may feel they are making progress but then suddenly face overwhelming grief again. This may occur at significant dates, such as holidays or birthdays, or without reason. Over time, these grief cycles will typically become less frequent and less intense as the person adjusts to his or her loss.
Tasks of mourning
Researchers describe the grief process as a series of tasks that the grieving person may work through to resolve the grief. One model describes four tasks of mourning:
Task one. Accept the reality of the loss.
Task two. Experience the pain of grief.
Task three. Adjust to life without the person who died.
Task four. Withdraw emotional energy (from the person who has died) and focus on other people and activities.
Factors affecting grief
A variety of factors affect the nature, intensity, and duration of grief:
The nature of the person’s relationship with the deceased
The cause of death. For example, the grieving process may differ depending on whether the person died suddenly or was ill for an extended time.
The grieving person’s age and gender
The life history of the person who is grieving, including previous experiences with loss
The grieving person’s personality and coping style
The support available from friends and family
The grieving person’s customs and/or religious or spiritual beliefs
In addition, the grieving process is often more difficult when the person who is grieving has unresolved feelings toward or conflicts with the person who has died. People who are struggling with complicated grief may find it helpful to talk with a counselor , such as a clinical social worker, psychologist, or spiritual counselor.
Grief in different cultures
Although each person's grief is unique, the experience is shaped by his or her society and culture. Each culture has its own set of beliefs and rituals for death and bereavement that affect how people experience and express grief.
The way a person expresses or experiences grief may be at odds with cultural expectations for bereavement. For example, someone who feels numbness or disbelief may not cry as might be expected at a funeral. Another person may experience a level of despair that feels out of step with cultural values or beliefs. Allow people to grieve in ways that feel right to them. Learn more about grief within a cultural context .
Grief and Loss 
National Cancer Institute: Grief, Bereavement, and Coping with Loss (PDQ®) 
CancerCare: Grief and Loss