He may not be going through withdrawals, but a return of the symptoms for which the medication was prescribed. This is based from this article -
"How to Stop Taking Zyprexa (olanzapine)
Your doctor should be recommending that you reduce your dosage of Zyprexa by 5mg a day every six days if you need to discontinue Zyprexa. Making it a week is just easier to remember. You can stop immediately if it’s an emergency, but I wouldn’t recommend doing that without a doctor’s supervision. The major problem with stopping antipsychotics is a sudden return of your symptoms." This is from this source (its worth checking out- I use it a lot) - http://www.crazymeds.us/pmwiki/pmwiki.php/Meds/Zyprexa
Wow, your little guy is on a ton of meds. I can certainly understand you wanting to reduce the load. Hopefully, you have taken the time to google each and every one of the meds. I have. They all do different things. Usually, you go off of one thing at a time - give the body a chance to adjust - and then proceed to the next med. That way you know what each med is doing or not doing. It is possible that Zyprexa is a med that he needs to function? Anyway, this is a very complicated situation and you do want to listen to your psyc - or find a new one.
I would also suggest that you check out our sensory integration disorder site - http://www.medhelp.org/forums/Sensory-Integration-Disorder-SID/show/1396. The
CL who monitors the site has a son with SIDS and has a ton of very helpful ways to help with this disorder. All of them do not involve medication. Speaking of medication - non of the meds your son is taking are for ADHD. But ADHD and SIDS also have very common symptoms.
Hope some of this helps. I will be glad to try and answer any other questions. But please check out our SIDS site - it is very, very good.