Sudden sleepiness and inability to focus?

I seem to have the same problem too. A lot of the time when I lose focus I think about very philosophical related things like "how the world works" or "the functions of emotions". If you're in a really boring class, what has helped a lot for me is to take out a notebook and make it look like you're taking notes but I draw instead. You might not be the type of person who likes to draw, so just like write down your thoughts or something. Or if you aren't into that just like fantasize or someshit. Put a positive outlook on the day, ya know?