If anything, fasting should help improve organ function because it promotes cleansing/elimination of toxins. However, there is always some risk because, during the cleansing process of fasting, the organs systems are taxed to an extent... it’s kinda like taking a few steps back (in terms of your health) in order to take huge leaps forward. This is the same principle with exercise – when you workout (or train competitively), you induce micro-tears in muscle tissue and even micro-cracks in bone tissue (hence post-workout soreness!); however, (provided you don’t overtrain and/or begin an exercise program too vigorously), you will ultimately become stronger).
Your time span seems fairly long for a first ever fast, but if you’re fairly healthy, I’d say go for it, but keep careful tab on how you feel... supposedly things get much easier after the 3rd day, and even easier after the first week.