Cutting his finger

Isn't there maybe something in the fact that he cut his finger badly? There must be some reason for it as it was brought up again when he spoke to his girlfriend. Is it possible that it had become infected and made him on edge? His friends told him to go and take a nap. I feel that this is potentially where everything went haywire. He was lying down which is the position we find him at the end albeit tied up. Infections make some people do crazy things and the hallucinations make sense with a severe infection. This may also be why we see the scene of him cutting his finger replaced with his friend cutting his hand to pieces and also why his crazy torturer chews offs his own finger.