Hi Fadeaway,
I've experienced this too. I call it my "delayed grief". I've found that the important thing is acceptance. I had to accept that my response to death is not immediate. It used to take me years to finally feel emotions and grief from the death of someone. I found out my uncle died in a freak accident and even though I was standing in the hospital with my family surrounding his body and everyone was crying, I felt totally numb to all of it. I felt guilty about not showing tears and questioned whether I was so beyond repair that I just couldn't even feel anymore. I judged myself on behalf of other people, assuming they must think this or that about me, and then drawing conclusions about myself from it, which was always negative. That whole process of judging myself just put up these mental walls of defense and made it even harder for me to feel grief.
Once I started accepting my grief process for what it is and stopped judging, the delay between a loss and a reaction grew shorter. It was a few months then a few weeks, now on death anniversaries I grieve a few days to a week later. It's easier to accept when you look at it as another biological process, rather than linking it to the blame game of "why did all these things happen to me to make me this way and why do I have to have those disorder" (at least that's what I used to do) because linking it all back in just feeds the disorder. Looking at it like metabolism for example, is better. It's a biological process that we can't necessary control and the speed of ours is not the same as the speed of someone else's.
Also, I started putting dates or anniversaries of deaths in my phone calendar to remind me, so when I started feeling all sorts of emotions out of nowhere I could look at the date and see if it was near the anniversary. This let me activity grieve, I was able to recall memories of them and cry it out which helped with the severity of the ptsd symptoms over time.
It also depends on how close you were to your pet. My cat was my best friend but I didn't even feel or cry right away when he died. It came later that night and throughout the following weeks. But I'd had him for 10 years. So anyway I'm sorry if this all sounds rambly, I just wanted to say I understand where you're coming from and it will get better, but just accept yourself and your own processes for what they are without judgement. I'm sorry for your loss Fadeaway. When you do feel the grief, know that there are people who do care.
Love,
Sammy