No man can keep working all the time. Forget 24*7, one cannot even work for 3 to 4 hours without a break.
So, when do you realize that you need to take a break?
1. When you find yourself stuck on the same page.
Often when the mind is not sufficiently rested, you find yourself reading the same page without anything being recorded by the brain, or writing a report but stuck at the same point for quite some time.
2. Facebook and Twitter start looking attractive.
After a long period of continuous work, you feel like logging on to Facebook, Twitter or YouTube (or nowadays Angry Birds) every few minutes. Almost unconsciously your hand starts typing out your FB username and password. This is the time to take a break. Its better meditate or go out for a walk than indulge in social networking sites.
3. You keep looking at the time.
To check how much time is left before you can leave. A man wanting to get out of office cannot do effective work. Either leave immediately (if your boss is a very nice man and lets you do so) or take a break, try to refresh yourself and come back for a short burst of work.
4. When you are unable to concentrate any more.
When after a long period of work, you are unable to keep going at the same pace, take a break. The mind suddenly starts thinking about a walk in the garden outside, or a coffee/washroom break.
5. When you are thinking about everything other than the work at hand.
Sometimes when you have other pressing things, or people, on your mind, it is not possible to concentrate on the task you are supposed to do. Either solve that problem first and put your mind to rest. If its not possible, tell yourself that you can do nothing about it, so its better to get on with your work. (Easier said than done though!)
Realize when your body is demanding a break and act accordingly.