How did Robin get hurt physically if Slade was just a hallucination?
So in the episode "Haunted," Robin is fighting with Slade. The catch? Slade died in Terra's volcano earlier. I understand that Robin may just be hallucinating Slade as a result of PTSD, but if that is the case, then how did Robin get so many noticeable physical injuries?
Most of what I saw from that episode was that Robin was stumbling down stairs, or getting thrown into walls (throwing himself into walls). However, those kind of impacts don’t seem severe enough to explain things like a swollen eye, torn clothing, or the sharper cuts and marks on his face.
I understand that Robin got injured from something like a placebo effect, but a placebo effect should not cause the damage that Robin had accumulated that episode. Was Robin just beating himself up while his mind created an illusion of combat in the form of Slade to make sense of the experience? Or was there a chemical agent from Slade as referenced in the end of the episode? And if there was a chemical agent, who powered it? It can't be Slade; he's dead.
(Also, this episode was one of my favorite in all of the show, but I've had this question for a long while)