I have the same problems. When I am eating normally I am often much healthier than when I diet. When I diet (1) often my period wants to begin (fortunately I am done with that) but this last time I felt like i was having a phantom period and (2) I get sick. in 2012 I started a liquid diet and 4 weeks later I got a terrible cold. And I NEVER get a cold.
But this last time I went to work after my week long absence and everyone was sick so... maybe it was just bad timing.
But this morning I am down 5 lbs. Tomorrow is usually a 36 hour fast but tomorrow I am not doing that.. I feel I am still recovering and that wouldn't be good. Also, my blood tests came back last week low in calcium. I redid them this Saturday so I want to get the ok before trying another long fast.