Hello darling.
I am so sorry you are having these symptoms, that must be awful for you. Firstly, I just want to reassure you that your mother can't simply take your child away, trust me my mother tried and it didn't work. They would have to prove you are completely incompetent and that isn't the case.
Secondly, what tests have the doctors done? You might be best finding one you like and sticking with them rather than constantly moving around, consistency is surprisingly important with ongoing medical issues. Have they done bloods, blood pressure, air flow tests (just where you blow into a tube to help see if you have asthma etc), scans, ECG's etc etc? Do you know your pulse rate and blood pressure?
While you are working on this issue, I think getting your anxiety under control is very important and may improve some/ all of your symptoms. I understand how stressful this must be for you.
It might be helpful to do a diary for your doctor. Write down everything... what you are eating, how much you are drinking (and how much you are weeing... you need a jug I am afraid!), how often you are having bowel movements, how much you are sleeping and if you feel refreshed in the morning or still very tired, and is your sleep broken? Write it all down.
The more information the doctors have, the better. Try to do it for at least two and preferably three or four weeks.
The good news is that kids are remarkably resilient, your son will be absolutely fine so long as you don't make a big deal out of these 'attacks' when they happen.
It is possible that all these symptoms are caused by anxiety, you may be having panic attacks, and if you are most tests would come back normal unless they took them during the attack. So please see your doctor about the anxiety, I think it will help regardless.
Trust me I know you're not making this up. Sometimes my family can get fed up with me when my anxiety is at its peak. I feel like nobody can understand unless they've truly had anxiety. Or a very open mind.
First off your mother can't take your child away without any proper legal paper work. Second off in my experience anxiety can cause dizziness along with allergies these days! Do you think your anxiety can be causing your dizziness? Do you have a doctor you can trust? I bounced around from doctor to doctor and finally found a great one. Have you tried therapy or medication? Or have you considered letting your son stay at your moms while you figure everything out? I'm not saying this is something you should do by any means. Just thought I would ask. If you put in hard work everything will work out.