How can a hallucination hurt you?

I was playing guitar on my bed and I hallucinated while playing and my guitar strap turned into a snake which began to coil around my neck so I took it off and then I looked at my bed and I saw little hills forming under my blanket which were popping up closer and closer to me as if something was under it and was trying to get me then a snake formed out of the material of my blanket then it plunged it's head at me and bit me and it actually hurt.