I figure I can relate first hand some of the dark side but have to be careful to not talk as if I know how my wife actually felt. Some times she tried to explain what was happening and so I had a bit of an idea. My own observations clearly showed that she was having a crappy time.
I think I'll write as topics or prompts remind me of various stages of those miserable years. My comments will be from the viewpoint of a husband, father and carer. This may not sit well with those who have, or currently suffer, with post natal depression. I don't want to offend anyone but being on the husband, father, and carer side comes with its own difficulties and mountains to climb. I wasn't the perfect one when it came down to filling these roles, but I tried. I tried and also failed. I didn't like what was happening and I couldn't fix it; I generally like fixing things. This was a case of helping, watching and being patient. I was also completely out of my depth but didn't know it.
Mostly, my wife could not or would not, answer the phone. Seeing who was at the front door was definitely out. When she was particularly bad this didn't surprise me but this behaviour/habit continued for many years. At one point I had trouble walking out the back door without clearly making sure of my intentions (ie not leaving her alone).
Sure, the phone and door weren't huge problems for me, but put them together with 3 young kids, a house to run, a wife to watch (4th child really) and the little things can add up over a period of time, a cumulative frustration I could do without. The phone and the door were tough things for my wife when she was down, just too hard, perhaps scary. The phone would ring beside her and she wouldn't pick it up. Facing someone at the door wasn't on at all.
From my perspective, phones, doors and people were obstacles my wife couldn't confront. Therefore, these little extras always went to me and perhaps this started a pattern of living which continued past it's use by date.