Postby Javizy » January 16th, 2011 4:15 pm
When they mean 'to sleep' they're interchangeable, but you can use 寝る to mean 'go to bed', 'lie down', and 'sleep with (someone)' too.
寝るよ!
I'm going to bed.
ベッドに寝て本を読む。
Read a book while laying in bed.
私は上司とは寝ていません。
I never slept with the boss.