I used to smoke weed to help my anxiety and panic disorder, however I had to stop because I accidentally smoked laced weed. I was on holiday when it happened and I started hallucinating, my heart felt like it was beating really slowly (sometimes it felt like it would even stop for a couple seconds) and I was literally passing out and I kept waking up. I started screaming for no reason, then started laughing; this went on for a good couple hours. I forced myself to go to bed because I was too scared to be awake. The next day I was having trouble breathing and my lips were blue. I was too scared to go to the hospital as I was only 15 at the time (I'm 16 now). I always used to have panic attacks, however after this event happened, they were 10 times worse. The pain in my chest was unbearable and it literally felt like I was having a massive heart attack as the pain would run down my arms and through my neck. It got so bad that a couple months later I HAD to go to the hospital. They told me it was just anxiety and that nothing was wrong with my heart (they gave me an ECG). It's been almost a year and sometimes, out of the blue, it feels like I'm "there" again. The same feeling of being helpless and feeling like I'm high and that there's nothing I can do about it. It's like I'm not even here. The longest it's lasted is about an hour. It honestly feels different to a regular panic attack as there's no physical pain and is just more of a feeling then anything. Yes I know it's my fault as I shouldn't have been taking anything in the first place but could this be PTSD?
I'm gonna be honest, I'm not 100% sure a bad trip would qualify you for the first criterion of PTSD - this requires you to be either directly or indirectly exposed to death, real or threatened serious injury to yourself or to someone close to you, or sexual violence, or be a first responder/police, etc exposed to a lot of heavy details of murder, etc. You might be struggling with an adjustment disorder if it isn't PTSD though, or something else entirely. I would definitely see your GP and ask for a referral to CAMHS though, because either way, this was a traumatic experience and you need to work through it and process it, because it's clearly on your mind a lot.
Having said that, I'm not a clinician, I've just spent a lot of time learning about PTSD/Complex PTSD with researchers whilst I was studying at university and also learnt about it being in therapy as I suffer with complex PTSD.