Hi Oopsyloopsy! Welcome to BL forums!
To actually "get a better understanding" of what your 17 year old is going through, I strongly recommend a child counselor. They are experts in child psychology and will be able to better assist you in that matter. Our community knows certain drugs better than most counselors do, for example, the new RCs which were not in use when the practitioners themselves were younger or in training. I'm not familiar with what Itizelam is, did you perhaps mean Etizolam?
Seizures are definitely a symptom of benzodiazepine withdrawal. LSD does not have withdrawal symptoms (To mine and modern scientific literature's knowledge), so I'm certain that this was caused by the benzodiazepine withdrawal. You have to had been addicted to it for a very long time to get to that stage, where you get a seizure from withdrawing cold turkey. This factor must not be ruled out by anybody who is now diagnosing him as an epileptic. The anxiety/panicky states are fluctuations that can be attributed to benzodiazepine withdrawal as well, which is absolute hell, and can lead to not knowing what is real and what is not real. As for the "strange feelings", those are is his receptors recovering from the MDMA.
Yes, at that age, his brain is still recovering, and the damage could well be permanent, should be carry this into adulthood. However, the sooner you stop, your brain will find a way to heal itself, it will take time. However, stopping benzodiazepines cold turkey is a serious mistake. People get emotional about their addiction and try to let it go all at once, and it can have severe consequences. These substances were created by big pharma to get you hooked, it's not easy to come off them. I recommend a gradual taper, buy a pill splitter and taper very, very slowly. He only needs to taper from the benzodiazepines (to my knowledge). LSD he can stop right away without worrying about withdrawals. For MDMA your brain has to recover from it slowly, so you need time off the drug sober (Get 5-HTP capsules from Amazon to help keep your sanity as you recover).
I'm not sure about the codeine though. Perhaps another bluelighter can help me out in terms of what he can do.
I hope this helps,
I understand it can be a pretty traumatic experience coming off benzodiazepines. In my case, I was forced onto them in a psychiatric ward and I got addicted. I never took that shit after I got out, and it took a massive toll on my brain.