HellbentA friend of mine with ADD that is doing a double major in physics/compsci taking 6 classes (~80hours/week) so I would say that might not be a factor if you really want to do well. He does do his midterms and finals in another place that gives him more time to do it because of his ADD, so maybe you could do that to get some extra time on exams.
One of the biggest things to realize is exactly how much work you have to put in. At my uni at least, to be able to grad with a bachelors with just 1 major in 4 years requires you to take ~65hours/week of classes in half of the semesters. To put that more into perspective, that's roughly 8 hours/day 7 days a week. Add that on to your job(s) and it can get hairy real quick.
You really have to be prepared to put in that much time and I believe a lot of people coming into it expect not such a high workload.
If that's what education is in your country is like (I doubt it actually is), the only right course of action is to emigrate immediately. There is no reason for people not to come into it expecting "not such a high workload", because anything other than "not such a high workload" is completely ridiculous.