Some do suggest it is a good idea to not jump into a fast but to wait until the body is ready for it. The body tells us when it is ready for a therapeutic fast by symptoms such as raised temperature, lack of appetite, dry mouth among others. Doing a juice fast or just eating raw can bring on a detox crisis which can naturally lead into a fast.
It does sound like you were in ketosis already though, after three days not eating and the symptoms you describe it is pretty likely you were. Hopefully the juice and/or raw eating will help you ease into the fast easier next time. Raw foods have always made the transition from eating to fasting easier for me.
Is your chiro a traditional back breaking one that makes you feel crap for days after you go or do they do the manipulations gently? If it is a traumatic experience going there may be other options out there for you. Cranial osteopathy I think is a good option worth looking into.