No I haven't had an EMG, and I had a spinal tape done approx 3 years ago and it was normal. Im not sure what they tested for as it was regarding intracranial hypertension suspected from a separate issue.
I have previous fatigue, pain and some intermittent muscle weakness due to over exertion and due to severe migraines. Hence, the diagnosis of M.E/C.FS & Fibromyalgia. This however is very different, its instantaneous weakness and it is prolonged where as the " other" is due to overexertion i.e "grind down malaise"
OK. We can continue after this but for now I don't think MS or ALS has been ruled out in your case.
I'd repeat the brain and spinal MRI, do a spinal tap, get nerve conduction studies and EMG's and consider a muscle biopsy to fully rule out both of those.
I highly suspect ALS from what you've said but you need further testing