[CyberFonic]

Sounds like a serious problem. From your description there is most likely an underlying medical reason for your difficulty in maintaining concentration in meetings, classes and when faced with reading and understanding code.

What exactly happens? Does your mind wander? or do you feel tired? Do you drive? if so how is your concentration on longer trips? How is it that you are better able to learn at home? What is the difference?

As @Topgamer7 suggests you might be suffering from sleep apnoea. Another possibility is early onset of diabetes. Anyway, you really should see a GP who will most probably refer you to specialists.