Oh good, I'm glad @lilyc29 mentioned modifying it. I used to follow the standard 25-minute timer exactly and it just made me anxious. Now I set a simple phone timer for 45 minutes when I'm really in the zone, and I only take a break if I actually feel stuck. Sometimes that break is just five minutes to make tea, not a full 15. You have to tweak it until it actually helps you instead of boxing you in.