Once you have formed a habit of writing notes and checking those notes after class, you can forget trying to remember whatever it is that has popped into your head. Feelings of boredom come from you, not the class. Nothing in and of itself is boring. Curious students don't close off from material they recognize. Rather, they listen carefully to see what more they can learn.
Curious students stay engaged with the message.
Bad habits can be changed. Learning to be an active rather than a passive listener will go a long way in helping you to increase you ability to concentrate. Listen with the intention of relating what the main points of the class were about. Plan to tell someone later about what you learned. You get a bonus here if you actually do it.