Give your brain a break by working in chunks. Try working for 45 minutes to an hour and then giving yourself a 30-minute break. Or if you prefer longer chucks, try working for 2-3 hours and giving yourself an hour break. By scheduling your breaks ahead of time, you can prioritize your downtime to ensure you are not cheating yourself out of much-needed rest.
Physical activity boosts blood flow and brain function, so to avoid working during your downtime, try going for walks or different energy-boosting activities. Also, when working extra to meet strict deadlines, be sure to add more rest to your schedule to replace the energy expelled working to meet those due dates. Positive anxiety is brought on when we have to work within time constraints, but they need to be counterbalanced with appropriate amounts of recovery.
Learn the times when you are most creative and protect those times. Block slots off on your calendar where you can get the most done, and consider guarding against interruptions by refraining from responding to emails or putting your phone on Do Not Disturb during that time. It may take some adjusting, but reorganizing your day to increase productivity could be worth the effort.