My own experience as a person with a history of PTSD, attending a 10-day retreat: I experienced both hallucinations and some scary delusions, but I was very committed to seeing the process through so the scary stuff passed quickly. The benefit far out-weighed the negative. But only you can know if you are ready to face your toughest moments or not. I do know this: I was not the only person on the retreats who had strong emotional stuff come up, and everyone seemed to survive it okay.
If you are on any medications, or if you disclosed the PTSD diagnosis on the application, the assistant teacher will probably contact you and ask clarifying questions to make sure the retreat is appropriate for you. Don't be intimidated by this, and use this as an opportunity to create a safety plan for yourself. It might result in the AT making some special appointments with you as a check-in, or making some other special arrangements. [I chose not to disclose my PTSD on the application, and that meant on my first retreat I was alone with the scary stuff. Looking back on that experience, and having the experience of having served on some retreats and seeing the special accommodations made for some people. I think I would have benefited a lot from having the AT know my situation...]
"As I am, so are others;
as others are, so am I."
Having thus identified self and others,
harm no one nor have them harmed.
Sutta Nipāta 3.710