Strangulation, in the normal sense of the word, isn't really possible. However, if the neck seal on the suit is not properly trimmed, it can be tight enough to cause carotid sinus reflex. Basically what this means is the neck seal exerts enough pressure on the carotid arteries in the neck to cause the heart rate and blood pressure to drop. This could cause a person to pass out. This would only be a problem in a new dry suit or when a neck seal has been replaced. Any experienced dry suit diver should know about this, though, and know to either order a neck seal that fits correctly or to trim it back to where it fits correctly.
