I'll compare three types of grief because there are a lot of types of grief, and also put down the seven stages of grief as well. Also, remember that if someone is grieving they are not always grieving over death, they might be grieving over an ended relationship, a missing person, or a traumatic experience (grief or trouble coping).
ABSENT GRIEF
Absent grief is when someone shows no signs of griefs and acts like it didn't happen, not because they are avoiding it, but because they are still in shock and denial. Unlike traumatic grief, they would express it as much and might need to go to a counselor to come to terms that their loved one is deceased.
TRAUMATIC GRIEF
This can happen when the cause of death or the events leading up to death were so horrific that the person cannot go on throughout their day or grief without feeling great distress, they could have panic attacks, fits of anger, or an episode of depression. Their brain might rewire themselves to hallucinate a lost loved one to cope. This type of grief can happen when someone finds out that their loved one was found dead after they went missing, after a terrorist attack, or if they were murdered, killed themselves, or if they say them deceased at the scene of the crime.
CHRONIC GRIEF
Unlike the two other griefs, chronic grief can be a type of grief someone never gets over or takes a long time to get over. Instead of learning to cope with their grief, it will only get worse and they will not progress through the seven stages of grief, and may never fully be able to accept what happened or move on. Sometimes this can happen when someone's child goes missing, the parent is scared of what is happening to them (Did they run away? Are they still alive? Are they being trafficked? Will I ever see them again? What did I do wrong?) and the longer it takes to find them, the longer the grief will last, which can make it chronic. And if after years of searching and they find out that they're deceased, that can make them stuck at one of the stages, or even go back, making their situation worse.