Complex grief   (Image Source)

After losing your parent, grieving is a difficult task in any circumstance, but especially if he/she was neglectful or abusive.  If you have not been able to work out the relationship with your parent before they die, then the grief you experience can be complicated grief.   Sometimes there is  so much unfinished business because your parent may not have been willing or able to do his or her part of the work to repair the relationship.  This can be especially true if there has been sexual, physical abuse, and/or substance abuse  in your relationship.  Death is so final that it can flush out feelings and behaviors you thought were behind you.
What is complicated grief?
There are different definitions at the current time, but generally speaking it refers to considerable grief that lasts longer than an average period of time. It is right to ask what an average time for grief is, and I don’t know the answer, but there are times when grief is profoundly disruptive of normal life and continues to impair day-to-day living for an extended time period.  There could be serious depression, panic, or even physical health symptoms that don’t go away with time.  Grief, trauma, and post-traumatic stress can be related and overlap.
There is help for traumatic or complex grief, including psychotherapy, somatic therapy, EMDR (two techniques that specialize with healing trauma), Dialectical behavioral therapy, medication, and more.  It is really important not to give up on yourself and not to isolate.  If you are depressed, it can be difficult to motivate yourself to reach out for help, but keep trying!  You deserve to get help and you are not alone.