Hypogylcemic or something worse?

I am on day 6 of the pre-op diet.  Yesterday, which was the day after they placed the IVC filter,  I got up feeling great, resumed regular exercise (riding bicycle) and washed my car, had tons of energy until about 2pm, then crashed.  I had a protein shake snack, and still did not feel better.  By the evening I called the doctor because I was convinced the filter had moved or something horrible like that - I felt so bad, light-headed, weak, just did not feel right.  He suggested I might be hypogylcemic and to drink a glass of juice and up my H2O intake, which I did, and I did start to feel better. I need to know what to incorporate into my pre-op diet to prevent this from happening again, I would really appreciate some suggestions.

I am not sure what your pre-op diet includes, so I'll try to give you some general advice, hopefully it helps. Many overweight & obese people have a lot of insulin floating around in their bodies. This happens with excessive weight and your body is used to a lot of food. Your body just thinks it always needs to pump out extra insulin. Now that you are on the pre-op diet (and likely very limited intake), your body is still pumping out all that insulin even though you don't need it. Extra insulin will drop your blood sugar (hypoglycemia). Eventually, your body will figure this out and stop pumping out extra insulin, but in the meantime, try to eat a balanced meal. Again, I don't know what your pre-op diet looks like (is it only liquid?) - but try to eat a balanced meal - 3 oz meat, 1/2 cup starch, 1 piece fruit, and 1 cup or more of vegetables at a meal. If you are feeling hypoglycemic, you may want to try eating a yogurt or drinking a glass of milk. Eat yogurt or milk when you feel the hypoglycemia coming on, and if it helps, follow it with a small snack (such as 4 crackers with some cheese or peanut butter). If symptoms get worse, go for the juice or candy. Typically, you can combat hypoglycemia better with milk or yogurt followed by a snack rather than juice or candy. Unless, of course, your sugar is really low (< 50) and you need a fast boost (juice or candy). Gosh, I hope that made sense.