Hard to cry...

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2 yrs ago when my grandfather died I didn't cried at all. I don't know why it happened, I was sad, but my tears just unable to flow out. Now it's also hard for me to cry, but when I feel stress I always dream about something sad and I really cried in my dream until I awake. I don't know why it happen, am I normal? Or maybe the older we are the more difficult for us to cry? Or...It just only happened to me?