Dude.

  I can't gather the motivation to practice any 
  skill that I'm not already naturally good at, 
  even when I really really want to be good at 
  that skill. 

Symptom of the universe. Most people really want to be good at things, but just flop through life like a fish out of water. The world is mostly like this.

  Similarly, I can't take care of pets, or even 
  plants; 

Yeah. That's normal! I have chit chatted with so many pet owning city dwellers who have explained to me how stressful having a dog is, to the point of taking valium. My mom killed plants regularly throughout my childhood, and still does. It's a hobby. That's how it works.

  I can't be anywhere on time; 

No one can. It's not a disease. Punctuality is actually hard. It requires serious dedication. That's why it garners high degrees of respect.

  and I forget at least one thing I absolutely 
  need to bring with me every time I leave the 
  house.

Yes. Normal. So normal, that stand up comedians earn millions of dollars helping people realize how normal that is. People don't laugh at those jokes because they're fraught with bizarre and alien concepts.

Meanwhile, the relief you describe is the very premise of stimulant addiction. Stimulants make people feel like capable superheroes on the up, and miserable incompetant failures on the comedown.

That is how speed works. That's why people like it. You don't have a disability. You just like speed. Everyone likes speed. Lab animals like speed, and they have no social obligations.

If you ever learned how to cook meth, while taking your meds, you'd probably never come back.