Go to sleep and Nod off

Go to sleep verb - Prepare for sleep.

Nod off and go to sleep are semantically related in drop off topic. In some cases you can use "Nod off" instead a verb phrase "Go to sleep". informal substitute

Nod off verb - Change from a waking to a sleeping state.

Go to sleep and nod off are semantically related in fall asleep topic. Sometimes you can use "Go to sleep" instead a verb "Nod off".