Asphyxia
From wipipedia.org
Asphyxia or suffocation is a condition of severely deficient supply of oxygen to the body. In the absence of remedial action it will very rapidly lead to unconsciousness and death. Asphyxia is a very real danger in scenes involving bondage and/or gags for this reason victims should never be left alone whilst bound. Furthermore, the binder] should always have a mechanism for releasing the bound person quickly if they get into difficulties.
