Feeling angry enough to slap people after your child has died is not something that can be considered Reasonable or Unreasonable, imo. You feel isolated and alone, and as if your world has ground to a screeching halt, while all around you life goes on and people bumble along, irritating you and angering you often, and sometimes managing to get it right too.
Sometimes irrational things can help you -- the worst year of my life, after going through the death of 2 family members, and returning to where I lived with no-one there who knew either of those whom I had lost, no-one to reminisce with about them, I remember counting down the last days of December and telling myself I'd feel better once the new year arrived and that horrible year was over. If someone else had told me I'd feel better once the new year came along, I'd have been spitting nails.
There's no wrong and no right way to feel, and no timetable. Losing someone, and how you respond to it, is a completely individual thing, and often the loneliest experience you could ever go through, even with sympathetic friends and family. Only you can get up each morning and be you all day, carrying that load around in your heart. There's nothing fair or even close to perfect in this life, and grief ultimately must be borne by each person on their own.
However, there is help available if the anger persists, and if it's accompanied by other problems with daily functioning or relationships. One of the tragedies of grief is that it can lead to depression.