Is the full nelson lethal?

i read in alot of places that it can break someones neck but there are alot of videos on youtube of people being put into full nelsons and the other people pushing down on their necks. lik a year ago some kid can up behind me and put me in a full nelson. then he pushed on the back of my neck and it was really uncomfortable. i told him to let me go but he held me there for lik 30 secs then he let me go and my freind told me it could be used to break someones neck.