
*Spoiler*
He OD'd. If you read the last chapter, they find out about Chase taking multiple drugs just to calm himself and for his insomnia since he doesn't sleep with anyone for pheromone release.
This will happen twice but the other one is a withdrawal symptom since he suddenly stopped taking them once he got with Josh.
This is an important part since Josh will suckerpunch Grayson after the doctor's appointment later in the story.

Sorry Hun, I read it last year and I used Google Translate to fry my brain so I don't remember much about chapter numbers.
But it happens closer to the final chapters. Chase got cocky since him and Josh became an official couple so he thought he doesn't need his meds anymore so he went cold turkey but his body went into a withdrawal and it caused trouble on set. I don't remember how Grayson got there but they talked about Chase with the Doctor and I think it's the part where Josh learns that the dog rumour and trauma came from Grayson so Josh got super mad and just punched him then left. I really loved that scene and laughed so much. He honestly deserved it.
Dang, what happened to Chase??? Anyway, I'm distracted—Naomi is so pretty