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 while bound. Furthermore, the binder should always have a mechanism for releasing the bound person quickly if they get into difficulties.
