On the anniversary of a loss or traumatic event, thoughts and feelings about the experience may be reactivated, with a resulting increase in symptoms of anxiety, grief or depression. People are likely to remember the event more clearly and experience the associated emotions much more sharply. This is a natural and normal part of healing from loss and trauma, although it can be quite distressing.
The symptoms anniversary reactions provoke are the same ones that the person may have experienced at the time of the loss: sadness, tearfulness, loss of appetite, trouble falling or staying asleep, nightmares, irritability, difficulty concentrating, feeling disconnected or detached from others.  Reliving these emotions are part of the healing process and actually facilitates recovery from the event. Everyone grieves differently, however, and not everyone reacts in the same manner. Some may not experience anniversary reactions at all, which is also completely normal.
For those who do experience an intensification of mourning on anniversaries, the American Psychological Association Disaster Response Network recommends some coping strategies that help:
Recognize and acknowledge feelings you may experience. Understand that your feelings are part of the recovery process.
Find healthy ways to cope with your distress. Share memories and feelings with someone you trust or just spend time with friends and family. Activities that allow your mind to focus on something other than these memories are a good coping strategy for some people. Contemplative activities like reading, thinking or just taking a walk are also a good approach. Avoid reactions that become part of the problem such as drinking or using drugs.
Engage in an activity that honors lost loved ones. You may want to plant a tree in their memory, make a donation to their favorite charity, participate in activities your loved one would have enjoyed or share happy memories with others. Consider volunteering; you may find that helping others actually helps you. 
Use your support system. Reach out to friends and family. Don’t isolate yourself. 
Some people will also benefit from speaking to a psychotherapist about their experiences. Psychotherapy may take many forms but will probably involved talking about the event or the loved one and learning new ways of thinking about and managing thoughts, feelings and behaviors that are associated with the experience. To learn more about this and other topics about your mental health you may visit www.apa.org.
Nancy R. Soro, Ph.D.