Am going on a ten day water fast, any tips please :-) ?

I have been feeling extremely weak, lethargic and fatigued of late... No illness, blood work normal and i also pack on multivits, iron supplement, eat and sleep well... So i guess its an excess of caffeine creating havoc in my system... I plan to go on a ten day water fast with no caffeine, green tea or coffee which i used to gulp down a lot... Does it actually work ?? Help detoxify and energise ?? Any tips and support?