My standard reply when questions like this come up: If you can't stay focused, you may have an unrecognized health issue contributing to the problem. I have a really serious health issue and while very ill I fucked around a whole heckuva lot on the internet/computer. The healthier I get, the less I do the aimless futzing around type stuff. But, to this day, I wipe my computer/keyboard down (both at work and at home) before getting on it. I react pretty badly to dust and stuff. An unclean keyboard/work area can put me in a fog and make it impossible to stay focused.
Like others here have said: Eating right, controlling my blood sugar, and so on also contribute to my ability to remain focused. When my mind starts wandering at work, I get up, go to the restroom, and get a new drink and/or snack. Then I am usually good for another hour or two. (If your health issues are less serious than mine, I assume you probably won't need such frequent intervention.)
Like others here have said: Eating right, controlling my blood sugar, and so on also contribute to my ability to remain focused. When my mind starts wandering at work, I get up, go to the restroom, and get a new drink and/or snack. Then I am usually good for another hour or two. (If your health issues are less serious than mine, I assume you probably won't need such frequent intervention.)