The body and mind have a remarkable ability to heal, beyond what most think is possible. It sounds like a lot of your mental condition is due to over-medication with pain killers and medicine, as well as stimulants like caffeine pills. But obviously a lot of it is the result of suffering from that traumatic event you had and the fact that you're still not completely healed from that. Trust me, I've been there with drugs and performance enhancing stimulants, it's not a long term solution.
I've also been through a very rough period in my life where my mental functioning was severely degraded from a traumatic event. For context, I was a software engineer and yet all I had the capacity for was to watch TV and browse the internet (I definitely couldn't study). I felt very fearful that it would be permanent and that my life was over, given that I depended on my intellect for my living (and identity). I even considered just giving up software engineering entirely to do something simpler, like retail.
Thankfully, having come through that period of my life, I'm now actually clearer and mentally sharper than I was before I was injured. I actually do run an product engineering agency in addition to doing a startup, and it helped a lot given that I didn't have to be somewhere 9-5pm, and I could take days off whenever I was feeling tired or needed to rest. I found that doing mentally heavy work didn't help my recovery as much as simple exercise like walking, and spending time in nature. I would echo some of the other comments here talking about the relationship between physical health and mental health.
www.stultusstudios.com
I recommend looking to practising some kind of Yoga, Tai Chi or Qigong. These practices are especially good for people with persistent and lingering conditions. Remember, that you are not "brain-damaged", having this self perception is very limiting. I'm not your doctor but this sounds like the after effects of trauma to the head, which is temporary and will heal over a year or two. I wouldn't write off your career aspirations just yet, you're very young and have plenty of time. Also remember that you can come out better than before as long as you focus on self care, rest and not pushing yourself too hard. Your rest and recovery is more important than grades. You don't want to exacerbate your condition and delay your recovery by overexerting yourself.
You're a high achiever but sometimes we need to step back for a moment to regain our foundation, so that in future we can flourish. Feel free to PM me if you want.