Wearing a noose-styl extender at max tension is the most dangerous thing in PE. The string is exerting a lot of force on a very small area, and this alone can damage nerves. Beside, blood is restricted, less oxygen, ischemia, nerve damage, you’re fucked. When you feel numbness, this process has already started, so repeteadly experiencing numbness can lead alone to nerve damage - which could be unrecoverable.