Set a timer for 25 minutes. Lie or sit somewhere with an eye mask on. When the alarm goes off, get back to work. Repeat until successful. Your body will learn

Set a timer for 25 minutes. Lie or sit somewhere with an eye mask on. When the alarm goes off, get back to work. Repeat until successful. Your body will learn that the "30+ minutes just to fall asleep" count against the rest time. The eye mask tells your brain it's sleepy time, and if you're at the office also tells others not to interrupt you.