I have had the same thing happen to me after surgery. I have an appointment with my Physician this week to have a glucose tolerance test done. Being in the medical field as a Paramedic, I have done a bit of my own research. I believe what we might be experiencing is Reactive Hypoglycemia. Here a a link from Mayo Clinic explaining Reactive Hypoglycemia http://www.mayoclinic.com/health/reactive-hypoglycemia/AN00934 . I think that you should see your doctor to find out exactly is going on in your body. When you eat or drink something with sugar in it, lets say a protein drink with added sugar! This causes your body to release insulin to breakdown the sugar and use it for energy. Your body is use to releasing a lot of insulin from when we were indulging in sweets before the surgery. So, your body continues to release a lot of insulin. Once that little bit of sugar is consumed by the insulin and used as energy, the body continues to dump out insulin looking for sugar that you ate. However, there is no more sugar there. Your blood sugars begin to fall below normal limits, your pancreas creates glucogon and tells your liver to break down the glycogen which releases glucose into your blood stream. This will cause your blood sugars to begin to rise to a normal level. Your body then releases epinephrine (adrenalin) into your blood stream this is what makes you shaky. Most people would eat or drink sugar to make their blood sugar rise. This will only make it worse in someone with Reactive Hypoglycemia the cycle continues.
It is recommended for persons with Reactive hypoglycemia, to eat small meals throughout the day including lean proteins and foods that are high in fiber. Make sure that you are limiting simple carbs and sugary substances. This will prevent your body from dumping too much insulin when you eat. If you are experiencing these symptoms make sure you see your doctor. I am not a doctor, nor do I play one on television. This is research I have done on my own that I am sharing with you. I have experienced many of these symptoms myself, and I have contacted my Physician for testing. Good luck, let me know what you find out!