I went on this cleanse earlier this year. I stayed on it 24 days and my dad 25 days. I felt wonderful. Around the 3rd or 4th day, I began having the headaches really badly. Like the response a few moments ago....Detoxing. Your body is killing off toxins faster than you are able to eliminate them....not a bad thing just uncomfortable. In the book a Sea Salt bath is mentioned. If you make that and drink it like suggested you will eliminate more and faster and reduce the discomfort. All the best!!!