First of all, great job in recognizing that you had a problem, what did it and that allopathy does not help. You have chosen a right path to heal yourself. Also remarkably you have already begun cleansing and healing by adopting vegan lifestyle also doing multiple juice fasting.
You will be totally fine doing short fasts with water only as long as you feed properly in between, take no drugs, alcohol or processed foods. If you eat raw fruits and vegetables of variety then you will build good nutritive reserves.
While fasting with water only it is important to rest, drink per thirst and stay warm.