I have never intentionally water fasted before, but there have been times when I felt ill or had a crises where I just couldn't eat. I also got very cold and had low bp during these times. Usually I would wear an extra layer of clothing so my body wouldn't waste so much energy trying to make me warm. Gentle stretching on the floor also helps get the blood flowing, but be very careful about dizziness.
A bluish tint to your nails? Please, please please go to the doctor. If you can't do this, find a pre-med student at your college, or a Science professor, or ANYONE who is more qualified to inform you. No offense to anyone on this board.. but we're not doctors as far as I know! You don't want to risk your health, even if you otherwise feel you can 'make it' without medical supervision. It is just too important to have all your bases covered. It could be something harmless.. in which case you can come back and post and reassure this worrywart that you will be fine! :) And if it is something harmful, then thank goodness you found out in time.