ConfusableLie or lay
To rest flat. No object needed. (lie, lay, lain)
I need to lie down.
To put something down. Needs an object. (lay, laid, laid)
Lay the book on the table.
Remember: LIE needs no object: you lie down yourself. LAY needs an object: you lay something down. Hens lay eggs; people lie down.
Quick check
I need to ____ down.