To nod off is to fall asleep without meaning to. Nod off in front of the fire, nearly nod off.
The head dropping forward is where the name comes from, and it is the sign everybody recognises. It is gentle and slightly comic, so nobody is embarrassed by it.
1phrasenod offTo fall asleep without meaning to.
“He would nod off ten minutes into any film.”
nod off is a phrase.
Practised in Phrasal Verbs