Give yourself time. You need to take regular breaks anyway. If you're having trouble with the tangerine check your posture. Sit upright at a desk and remember to breathe, also stick to the time frames and activation periods. If you say 30 minutes the stop at 30 minutes. This way your body gets used to the fact that you will be finished when you say you will be finish and not have to switch off to make sure that you do.
Also drink plenty of water, chewing gum will also help, this helps to get oxygen to the brain. Lack of oxygen is one of the reasons we tend to fall asleep.
Alex
