I haven't really tried ctb by doing it but at the beginning of this month I would have a rope below my Adam's apple and I would tighten it. I'd become unconscious within seconds and get seizures. I filmed it once and the seizures are sometimes mild and sometimes to the point where my entire body gets thrown backward. They last around 10 seconds until I become conscious again.
In my experience, it's much easier to stop the oxygen to get to your brain if you have a rope or similar below the Adam's apple. But you would also need something to not make it loosen up if you get seizures.