My first 3 days I felt sick (headache, nausea) and of course hungry. In fact the first day I tried I broke the fast at night. I started again the next day. No9w I´m on my 13th day.
I also got black outs, and someties still do. They always happen when I move too fast, for example, after sitting or laying down I get up in a jump or very fast move. I have read this is totally normal.
Take any necessary tests to see everything is ok. If it is and you are good to go, pick a time when you can rest for the 4 first days. Lay in bed most of the time. Make slow movements. Don´t be afraid of weakness, diziness and nausea, because if you´re healthy, these are just normal symptoms.