Definitely.
When I first started posting here, I was still horrendously raw from several experiences... yet recently, I was able to describe one of the worst [hemorrhaging post-op and being deliberately ignored and taunted by the hospital personnel, who were willing to let me die in order to prove I couldn't tell them what to do] - in a single paragraph.
Now I can describe it in 30 words.
A year after it happened, I had an 'anniversary reaction' so severe that for several nights I could not sleep if I lay down flat. I'd saved my own life at the time by curling up into the tightest ball I could manage, and sitting up throughout the night like that until the docs came in around 8 a.m. and I could tell them what had been happening to me. Lying down, I would have bled to death. So a year later, this terror of lying down to sleep came out of nowhere, and even when I understood what it was, it didn't go away for about four days - which is about as long as it took me to get 'out of the woods' when the hemorrhage occurred.
Now, I just think, oh, this is the day I had the surgery. How many years ago was that? Thank God it's well behind me now.
So desensitization definitely happens. And it happens a lot faster in a supportive environment.