What do you mean by "fast"? What are you taking in? Just water?
A body needs a certain amount of calories to function, and a balanced diet is best. What made you want to fast? Weight loss? If so, that's not the right way to go about it, and it definitely would explain the symptoms you're having.
Fasting is done for different reasons -- sometimes spiritual, sometimes for cleansing, sometimes, and this is the wrong reason, for weight loss. But no matter the reason, breaking a fast depends on if it was a total fast with just water or you just ate less. It sounds like you did a total fast, and if so you never ever start off a fast with things that are hard to digest. Meat is the worst thing to start off with. It also doesn't make much sense to clean your system out and then put toxins right back in, and meat unless wild and eating wild is a pretty tough thing to swallow. What you should start with is liquid, maybe some simple juiced food, and slowly build back up to a healthy amount of calories and a balanced diet. And I'd try to do all organic, why put back in chemical toxins if you've just gotten them out?
Good advise. I wondered what protein, like meat or fish, would do. I wound up breaking the fast after five days. I did a basic water fast, but... adding a small amount of fruit juice takes that funny taste of city water out.
My blood pressure dropped ten points on the upper number, and I could not remember the lower number, but it's now at 85, and usually it's 95 or higher. So the experiment worked.