dementia from the inside

I'm a fat person.  Usually that's not very relevant to this blog and thus doesn't get mentioned much.  I lost almost 100 lbs on my own but now I gained back a little so one of my doctors has sent me for "medically supervised weight loss" which basically means shakes and bars and hardly any "real" food--and no carbs.  I'm eating maybe 500 calories a day.
I don't do well on low carbs.  I get really sick.  I call it "carb dementia".  And of course, with no carbs and no calories in me, and exercising 5-6 thousand calories a week, I'm very sick.  And I've figured out why it's so very scary for me to be this sick.
I feel like, if I ever get Alzheimer's, this is what it will be like.  Except that I can't eat half a tortilla and feel better if I have dementia.  It will be like this all the time.  And when I have carb dementia, I know it. Just like my dad knew that something was wrong with him.
I know that:

• I am stupid  (my brain is hardly working)
• I am not comprehending everything I read 
• When I write, I don't always make sense 
• My spelling is horrendous (worse than usual) and I don't recognize it if I don't have a red line telling me
• Simple tasks like assembling an air conditioner, office chair, or IKEA furniture are nearly impossible
• My hands shake when I try to do precision tasks
• When I talk, I can't remember words or names (expressive aphasia, what my dad had)
• I can't remember the point of what I'm saying by the time I'm done saying it
• I'm perpetually exhausted and have to nap like an old person
• My moods are bad; I am mean-tempered and utterly lack patience 
• I am depressed; I cry a lot and sleep a lot and have no motivation to do anything
• I stumble over everything when I'm walking, even things no sane person would trip over like a piece of paper
• If I exert myself (such as shopping in a poorly air-conditioned store) I start to grey out and get tunnel vision (I work out in a pool so I don't overheat)

The thought of living like this the rest of my life is terrifying.  The doctors want me on this diet 18-20 months.  That's almost 2 years.  There is no way I can get a job or even look for one when I can't even rub two words together most days.  When I have to take a nap like an 80 year old after the slightest exertion.  When as part of this diet I have to eat their bars and shakes every 2 hours on a tight schedule.
For instance, it took me well over an hour to compose this blog post. It should have taken 20 minutes.  I have no idea if it makes sense.  There aren't a lot of red lines so everything is probably spelled correctly.
I have to wonder if it's worth it.  To give myself temporary diet-based dementia so I can live long enough to get real dementia. 
(image source)