Why is it when I start to cry I get shivers?

Why is it when I start to cry I get shivers.. shivers and I start to crackle my teeth.. I know it's not done by will it just happens. I tried to do it right now just like when I started to cry last night. Every other time I cry I don't get them. But last night was so bad I cried for 30 to 45 minutes. I just shivered and cried.. does anyone know why this happens? Thank you