On sleep, information overload, and simplifying
On sleep It's entirely too evident when you are tired because your behavior changes so drastically. I can't exactly fault you for that, as that's natural for anyone who has not slept sufficiently. Recognize, however, when you are in these states and do something to actively combat the slowing of your productivity. It may seem like a valid solution to simply "power through" and be tired for the entirety of the day, but you have experienced firsthand the lousy results of such an approach. You are still tired, less focused, more emotional, and less reasoned. If you would take 12–15 minutes to relax, rest your eyes, and not think, the rest of your day following that would go quite smoothly.
On changing your physical state Sometimes, like in the case of sleep, it's not that you need to become more focused or more disciplined in your work, but simply that you need to change your physical state. If you are tired, then you should sleep. If you are sedentary, then you should walk. If you are bored, then you should move. Put yourself in the desired state of mind by allowing your physical being to be an extension of that state.
On information overload There is a lot to learn in any given moment, and if you learn all that you can today, you will still have more to learn tomorrow. I have seen this discourage you from learning at all on some days, and on others, it has inspired you to learn as much as you possibly can in preparation for the extra learning that comes after. I caution you not to become overwhelmed by an influx of information that hasn't yet corresponded to action. You must pride yourself on the information and activity that you reject rather than accept. There are plenty of good ideas that you must simply turn away from because you have not fully executed on the ideas of yesterday. Slowly and steadily apply your learning to the tasks at hand.
On simplifying When you are first introduced to a new idea, it will probably appear complicated when in reality the idea is quite simple. You simply haven't understood the idea well enough yet. In order to take action on it, you must fully understood the idea, and to do that, I recommend you simplify. Your simplification does not have to be perfect immediately. You might be oversimplifying for a time, but if you never oversimplify you'll never get to the point of understanding all of the nuances and intricacies of the idea later on. Start small, and work your way up. Say no to the things that you don't need to know yet, and come back to them later.