I would agree in general, but it's risky to explain a scientific issue in so much detail, if the science isn't accurate. I'd recommend eliminating the explanation.
I agree with both @ChickenFreak and with @Okon -- I do find it very difficult to believe that they'd be able to predict the very specific behavior that the serotonin problem would create. However, if you write a really kick-ass story that's just so amazing and so compelling, then I could forgive the questionable premise as part of my suspension of disbelief. So yes, it's a problem, but it can be a minor problem if you rectify the other issues -- that is, that we really get to know him and get caught up in the story and believe him as a character.
Well, the character seems a bit wooden, but then so too does the prose. Unless you're writing from the point of view of a mechanical character, the sentences shouldn't be mechanical and choppy like they are in your firsta couple posts. And I would not have him describing himself as "I remember having..." because that's just not a thing people would say. Here's an example of how you could fix it: Now: I don't like mirrors. I have short, curly, brown hair in a crew cut. I have an angular face from my father. I have brown eyes from my mother. Suggestion: People always tell me I have my dad's angular jawline and all that, but I definitely have my mom's eyes. Brown, just like my curly hair. I like to keep that pretty short most of the time, but these days I always shave it down to a crew cut. See I got in a fight a while back and this other guy grabbed my hair and yanked out a big fistful, really gave a new meaning to havin' someone by the short and curlies, ya know? Anyway, nobody's gonna snatch hold of a buzz cut, so I keep it like that just in case. Added bonus? I never have to worry about styling it in a mirror; I freaking hate those things. Also, for the love of all that is holy: Your and You're, learn to use them properly. Hope this helps.