Is it normal that i can't cry?

A few weeks ago, I was in a situation where I believed nobody loved me, my life sucked, and other equally disproportionate reactions. I was feeling really sad, like, sadder than I had been in months. I remember reading somewhere that in the process of crying, your brain releases a chemical that makes you feel better, which is why you cry when you're sad. So when I got home, I stopped holding back tears, which is what I had been doing for months. (I take pride in my perpetual poker face) but when I stopped holding back the tears, no tears came. I tried forcing expressions, I tried making myself sadder, I even tried sniffing a vial of chopped onion I had in my cabinet to start the tears flowing. Once my eyes stopped stinging, the tears stopped. I had forgotten how to cry.

I remember crying in the past, usually because of pain or temper, I even remember faking emotional anguish to convince my parents to buy me that new toy. As I got older, I gradually stopped crying, believing it to be undignified. By the time I tried again, discussed above, it had been years since I last shed a tear, not counting watery eyes.

I've never heard of this from anyone else, and can't find an explanation. So, IIN?