I'm currently working as a full-time QA engineer. I have been working here for a little less than a year. I'm on the autism spectrum with tiredness issues and working full time is just too much for me.
My manager knows that I'm on the autism spectrum and have exhaustion issues (I told him some time ago, before the end of my probation period and he seemed okay with that). However, I'm not recognized by the State as a "handicapped worker"* yet (and it will take several months before I can have it). I do however have the backup of a doctor.
During my next big one-to-one meeting, I'm planning to ask my boss for a part-time (70%) but I'm not sure on how to do it in a way that will make him more likely to accept.
(So, I guess I'm basically asking for negotiation tricks)
About the negotiation
I'm not (yet) ready to quit if I can't have this part-time (I gave myself 2~3 years to successfully negotiate a part-time at my current job). If my manager says no to working part-time, I'm just planning on asking again in a few months (when I will have the official "handicapped worker" recognition and thus, a stronger case in my favor).
I will be fine with my manager offering just an 80% part-time (because it still would be an improvement) but it would mean that I will likely have to ask for less (70% or less) again in the future.
I believe that my manager will try to offer me to work remotely (maybe one day a week). But I'm pretty sure that this won't solve my issues and I would thus consider this a failed negotiation (which means I would have to ask for the part-time again in a not-so-far future).
I don't mind hiding parts of the truth when negotiating but I'm really not comfortable with the idea of bluffing.
In my last job, I tried to negotiate a part-time (60%) but I told them it was because I wanted time to write stories (instead of saying "I just want a normal life"). This didn't work (it made them feel like I wasn't invested enough).
Notes and clarifications:
My manager knows that I have tiredness issues but doesn't understand how much this impacts my work and everyday life.
My doctor supports part-time work as a long-lasting solution to the issue. However, this doctor isn't the "occupational physician" and I might need to see this doctor too before being allowed to work part-time.
I work in France under the French law.
* Autism is considered a handicap in many countries, France included.
This question might get better/different kind of answers than it would get on the workplace, but I have seen some similar (kind of) questions and the answers there weren't suiting my needs, which is why I chose to post here instead.