I've been lethargic with a headache the entire time I've been back at my parents' place. I blamed it on jet lag. Moments ago, I discovered two things: 1) The coffee I've been drinking is decaf, and; 2) I have a strong dependence on coffee.
Sounds about right. (Although, my experience with intermittent fasting for the past 10 years says something like strep symptoms get exacerbated by the fasting, so I'm guessing that felt quite bad.)