Inemuri (居眠り?) is the Japanese practice of sleeping on the job. It literally means, "sleeping while present". It is a way to show how committed you are to working. In other words, you spend so much time working that you sleep too little at home and have to do inemuri.
Rules of Inemuri
1. You have to stay upright to show that you are still “socially engaged”.
2. You have to be either high up or low down in the company.