This forum is for questions and support regarding
Down Syndrome issues such as Dental Problems, Communication Problems, Developmental Disabilities, Hearing Loss, Hypothyroidism, Immune System Problems, Learning Disabilities, Joint Problems, Muscle Weakness, Respiratory Disorders, Seizures, Sleep Apnea, Weight Problems.
i think first of all that you need to jump onto a mental health forum here as they can support you better than a DS forum, then you will likely find people who experience similar problems.
I also belive that the mind and body are very closely connected and our mental health plays a great role in our bodies health. it sounds like you have looked for physical reasons for your state of mind but perhaps you need to look at your mental health that is causing the physical issues? i am not calling you crazy by the way, you sound far from it and looking into your mental health does not make you mentally unhealthy either.
it sounds like two things could be an issue...depression or chemicals taking a toll on your mind and body. if smoking has such an effect on your body, you need to stop doing it! there is nothing positive to come from smoking and if it gives you direct symptoms then that is very likely a problem to your body.
perhaps talking with a doctor, councellor or registered nurse with a background of "holistic care" which is looking at the entire body, not just symptoms, you may find the answer.
good luck