As important as it can be to keep the model of the system you are building in "ram", it is actually more important to allow your brain to digest and process new

As important as it can be to keep the model of the system you are building in "ram", it is actually more important to allow your brain to digest and process new information with genuine downtime. The way I approach it is to "pulse" through the day with absolutely uninterrupted programming sessions of 1-2 hours interspersed with 20-30 minute breaks to allow time to digest. It is extremely important to maintain focus in the "on" times and not to feed new information into the wetware during the "off" times. For me, this required quitting reddit completely and limiting other news feed and communication quite drastically. The other key factor is to start your day producing instead of consuming (read about it here, as a matter of fact). Makes a surprising difference in your mindset. The end result? I can sustain a solid hours 8+ hours a day of real engineering for 5-6 days a week without running too serious a risk of the burnout you describe whereas before I would be lucky to manage 3-4.