Because it was too tired.
(Two tired i.e. having two tires (or "tyres", in British, Australian, etc English)
They LIE down (to lie, lay, lain). LAY the table, please! (to lay, laid, laid).
Get Down or Lay Down was created in 2000.
Lay Me Down was created in 2010.
It is not a combined form. The word "down" is an adverb. It can modify verbs such as lay.
Lying supine means to lay on your back with your front up and your legs in the air as if riding a bicycle, i.e. Supine Bicycle
The past tense of "lie down" is "lay down."
You can't lay down in clubpenguin. Sorry.
The past tense of "lay down" is "laid down."
"Lie down" is the correct phrase to use when talking about reclining or resting in a horizontal position. "Lay down" is incorrect in this context because it should be "lay" only when used with an object (e.g., lay down the book).
"lay" is a verb and "down" is an adverb.
Lay Down with the Strawbs was created in 2008.
Lay Your Troubles Down was created in 1989.