The judge lay down for a nap, then she got up and laid down the law. Or did she?

The judge did both correctly—grammatically, at least. Here's the whole story:

Wrong: She laid down on the shag carpet.
Right: She lay down on the shag carpet.

Wrong: Mom lays down for ten minutes every day after work.
Right: Mom lies down for ten minutes every day after work.

Right: He just wanted to get laid. (It's the idiom, so it’s OK.)

Summary of forms:
recline (intransitive): lie, lay, lain
place (transitive): lay, laid, laid
falsify (intransitive): lie, lied, lied