Its very hard to say.
Do you have an Autoimmune Disease...Hashimotos or Graves Disease?
If you show Alpha waves in your sleep, I dont think it would be connected in any way to Thyroid Cancer.
Obviously you have seen a Neurologist...what did he say about the seizures, alpha waves and the apnoea?
I would think that they are all connected to electrical and chemical impulses in the brain.
I dont have enough knowledge to give you a direct answer.
Maybe another member here can help with this one.