Having your arms raised up behind your back is one of the most intense bondage situations you can get yourself into. Not only does it push your chest out so your nipples are quite vulnerable but there’s also pressure on your lungs making it difficult but not impossible to breathe. The only real drawback is that because the human head isn’t exactly a light weight appendage, there’s a lot of strain on your neck so for long term bondage it needs to be secured back. Preferably with a elastic cord.