Hallucinations

I feel like I'm going crazy
I keep seeing these weird entities
I don't know what they are
But they won't leave me alone
I can always hear them
I can always feel them
I can always see them
And I always fear them
What are they?
I just want to know
They don't look like humans
They look much more frightening
It's incredibly hard to describe
And it's driving me insane
Tell me, what's wrong with me?