The insulin dumps are known as overshoots and with RH, the insulin drives down your blood glucose levels down and the quicker it happens the worse the symptoms. The lower your BG gets, the symptoms get worse.
The reason you feel awful in normal levels is similar to a sugar crash. Your brain is probably used to being in relatively higher than normal levels due to carbs and sugars, it wants to stay there, just in case there is too much insulin or too high a spike, so the brain reacts by issuing signals to stop the spike or wanting more glucose, when your brain gets a signal that your BG is plummeting down, it tries to defend itself, send more signals, more symptoms.
Your brain, when out of normal levels, lacks vital hormones including glucose, cortisol and so on. The high levels of insulin, means that the lack of glucose, your brain is sending signals to your body to correct it, but it can't because of the need for food to process into glucose is not there, unless you are in ketosis and using ketones.
Because you are not yet in control or in ketosis, the imbalance of insulin, glucose and other hormones have symptoms connected to it. There is insulin resistance, high levels of circulating insulin mean your energy levels are down, the brain fug, lethargy but much worse, because there is nothing your body can use to correct it, glucogenisis from your liver is very poor because of insulin resistance, hence this is why even though I was eating very little, I was steadily gaining weight. Symptoms are the brain's way of telling you something ain't right! Unused insulin turns into unwanted visceral fat around your organs.
You feel awful because of the signals not doing what your brain wants it too!
Your nervous system is connected to all your organs and glands. Your nervous system is why your symptoms include anxiety.
Without using scientific jafgon, I think that about sums it up!
Keep asking!