I was in the same boat as you I guess. My 3rd year of college doing a B.S. in CS was a critical point, but nows the time to make important decisions. Me, I choose to stick with it and go to graduate school while studying for various certs (studying butt off in lab for CCIE at present). Just because you have a CS degree doesn't mean you will be at a desk forever. There are plenty of jobs out there where you can have mobility and even work overseas if you wish (general dynamics being one that im familiar with) without staring at a screen for 8+ hours a day.
As for the headaches and blurry vision, well I think most of us have that at one time or another. And your logic issues...the only thing I can say to that is logic is something that just doesn't come easy (for most people) and needs to be developed. So just stick with it and it will improve.
My rule of thumb is stick with what you enjoy, and persue it to no end. Don't be discouraged and stay focused on what you want out of a particular career. I am sure you are no fool, so do some soul searching and decide what really makes you happy and go for it full bore (as long as its profitable lol).
Good luck!