I went through a period of derealisation/depersonalisation caused by a very bad relapse in my anxiety after my mum's death. As my anxiety got worse, my GP recommended changing meds - which did not go well, and I ended up on my original medication after about 4 weeks. In the last week before I restarted the original tablets I didn't sleep for about 5 days due to having recurring panic attacks in my sleep. I was so exhausted by the end of the week that I felt drunk, and nothing felt real. The recovery from this period took months, and for about 3 or 4 months nothing felt real - it was like I was in a dream and I did have moments where I wasn't sure that the world was really existing and sometimes even checked with friends that they were indeed real! I have lapses of derealisation fairly regularly, especially when I'm stressed or tired (I have a sleep disorder which can make me very tired, which is helpful).

I doubt you have PTSD, but I'm not an expert. It sounds like the onset of the anxiety issue.

You just have to remember that derealisation/depersonalisation is the brain's way of protecting itself when you are super anxious or stressed, even if this is subconscious. The best way to deal with it is to just let it be. I do grounding work on the days when it reoccurs, and it always passes.