Oh! I totally forgot (see?) relatively recently learning about the Pomodoro technique. Short version: set a timer for 20 minutes and do just one thing. Nothing else. No mail or Slack checking. Afterward, take a 5 minute break to do anything you want. This helps 1) decompose daunting tasks into manageable chunks, 2) give your brain a chance to replenish neurotransmitters and consolidate memories, and 3) remind you to periodically snap out of hyper focus and eat, stretch, go to the bathroom, etc.