Normal voluntary reaction to coming to the realisation that you're a mortal. It happens to all of us. I went through a very rough time with it, and no one would talk to me. For about a month, it was all I could talk about. Then my grandmother said something to me which stuck by me since.

"The way life is, you may die today, you may die tommorow, or you may die fifty years from now. But when it's your time, it's your time, and if you just allow yourself to not live due to being afraid, you're as good as dead already"

That really switched things around for me. Really made me fight back against the world and start actually living as opposed to simply exsisting.

Stay safe.