Since the Diagnostic and Statistical Manual of Mental Disorders probably contains something relative to the condition of being selfish or self-centered, Prolonged Grief Disorder could be included in this manual since there comes a point at which grief can become selfishness. For, according to psychologists, people cry and grieve sometimes because there is an emptiness in their lives by the final absence of a loved one. They miss their loved one for different reasons, but, certainly, one of them is the absence of the love of this person, the happiness and comfort this person brings, the opportunities this person provides the other, and so on. In other words, the deceased or departed has done things for the one who remains, and this person, sometimes, does not want to lose these benefits. Especially when the grief is prolonged, the element of selfishness becomes evident as the person is really feeling sorry for him/herself.
Mourning is a normal process that is undergone by people when someone they love dies. Grief is also normal. I do not think that there is a specific or allotted time to mourn. You can't just tell someone whom you think has been mourning for too long that it's "times up" and that they need to move on now. I think this is very subjective, but it is very important that the people who mourn, we who are left behind have strong and emotionally stable people around us in a sensitive time like this. Actually, we can help these people move on and carry on with their lives. Each of us has different ways to cope up.
Prolonged grief disorder being included in the DSM-V is still under debate. I am not in the position to say that it should or should not be included. In my opinion, it would be better to leave this to the professionals.
It really depends on how severely one is upset and the period one is upset for, but that is subjective. There is no common definition as to what is normal for grieving, so there is no definition to what is not normal.
I feel like everyone mourns for different times, and it all depends on who you are and what/who you're mourning and what effect they had on your life. I don't believe that you can mourn for too long because everyone heals in a different way. Prolonged grief disorder being placed is in the DSM-V is still being decided by professionals, and because I honestly have no experience with this disorder, I wouldn't want to say that it should or shouldn't.
When you lose a friend or a loved one, it is common to feel sad and mourn for a while. However, how long is "too long" may vary based on who it is and on how the person is acting. To be diagnosed with Prolonged Grief Disorder the symptoms would include anger, sadness, guilt, despair, overwhelm, denial, betrayal, emptiness, anxiety, and the decline of your general health. Since there is a lot of studies and information about the disorder I would assume that this could qualify for DSM, but it is still up for debate.