your head off
(one's) head off
Very intensely or loudly; with no restraint, hesitation, or inhibition. (Used after verbs associated with speech sounds, such as "yell," talk," "laugh," etc.) I'm telling you, Mark's boyfriend is hilarious! He had me laughing my head off when I met him. Suzy started yelling her head off when I told her she couldn't have an ice cream cone. A: "So, has Noah started saying any words yet?" B: "And then some—he's been talking his head off for months now!"
— your head offlaugh, talk, shout, etc. with a complete lack of restraint or without stopping.
1990 Paul Auster The Music of Chance Now that the kid was out of danger, he began to show his true colors, and it wasn't long before he was talking his head off.