What do i do if i have toothache when i lay down?

See a dentist: Tooth may have an infection. When you lie down the blood pressure increases in your head and neck, causing a throbbing feeling on inflamed tissue.

Vascular engorgement: If the pulp becomes inflamed, when you lie down the vessels inside your tooth become engorgeg ANS swollen, causing pressure against the hard tooth walls of the chamber, hence pain and throbbing!

Dental problem: Tooth decay with inflammation likely. Lying down increases blood flow to area, this increasing pain. See dentist for evaluation/treatment.