So can the lack of salt which one of the meds my son takes forces me to add extra salt in his food

YES.

Yes, I'm pretty sure it can.

I think it does!

Yes, it absolutely can while I am not a MD my Nana was a nurse for many years. She informed me that if it's to High it can cause the Neurons in your brain to miss fire. You might also have been born, with epilepsy and not even know it that's my case. Request to see a Neurologist first your GP needs to write a letter to your Health insurance provider then you should be able to get referred to a good neurologist.