I know it's probably health anxiety. 

For the past week, for example, when I open my mouth fully I have a very small pain. I have no issues/pain eating, speaking etc, but if I do it and I focus on it then I have some pain. Not sure the cause of it, and that terrifies me. 

My mind is going crazy. Maybe my jaw is broken, maybe this, maybe that, maybe it's even cancer.  Or an infection that might affect the brain in the long run. 

It makes me feel so afraid, and one mistake I always do is googling every pain I have, and then seeing all the possible terrible scenarios. 

It probably comes from my childhood, when I was 3 years old I had a leg surgery where I almost lost my leg. All I remember is the immense pain I had back then. Now I am 21 and those feelings will never stop. To the point where I will think about it now 24/7 till it and if it goes away.