At a certain point, he couldn’t even discern his hallucinations from reality, and he very nearly exposed his identity to the corrupt SCPD by the end of the episode.
He began hallucinating, seeing everything from a still-alive Prometheus taunting him to Felicity leaving him to the whole world turning upside down.
Oliver’s abilities as a vigilante were called into question in this episode.
Felicity, dressed in civvies and without backup, had to try and convince him not to head into what was either a suicide mission or a mission that would end with both of them exposed.