It's very dangerous, and I wouldn't recommend it to anyone who hasn't put their body through extreme circumstances in the past and knows their actual (not percieved) limits. I haven't pooped in a week, and my last bowel movement was gnarly.
A safer rate of weight-loss should not be more than 2 pounds a week, or approximately a 1,000 calorie defecit per day. An online search for a basal metabolic rate calculator should be a starting point.
Advice to others, no matter what process you take: I recommend not weighing yourself more than once a week - it's a mental thing.