Decide how much time the task requires, and how much energy. You may wish to include the task's priority level to help make this decision. Regularly plan time to relax and get it together. This time may range in units of 10 minutes to whole days according to your needs. You've earned this time off.
Exercise is essential for superior academic performance.
Your brain would not function well if your body is tired. Stress reduces performance. Something almost always comes up to derail your efforts. Allow for it. Floating tasks can be done anywhere, anytime.