Slowly easing into ketosis?

Hi,

I have chronic fatigue syndrome and want to fast. Each time I try, when I approach the 36-48 hours mark, I have a rapid heartbeat and a little difficulty breathing and weakness. So I also err on the side of caution and terminate the fast by drinking some juice.

I am wondering if it is possible to slowly ease into ketosis instead. So keep taking in a small amount of calories from fruit juice during the beginning of the fast and slowly reducing this quantity over a period of days. Presumably the body will then be in part-ketosis and part-glycolysis?

Any thoughts would be appreciated! Cheers

Mark