Never sacrifice sleep.

There is lots of scientific proof to back up the importance of sleep. Lack of sleep has been connected to weight gain, illness, memory and yes, productivity. It is an illusion; you think you are getting more done, but in reality you do things much more slowly than you would if you were sleeping right, and you probably make more mistakes too. So schedule 7-8 hours of sleep into your day and stick to it. You'll be surprised how things improve quickly.