Definition: To be in a position in which a person's body is flat on a surface such as the floor or a bed.
It's a classifier verb phrase, where the passive palm is downside, unlike the regular sign LIE-DOWN whose passive palm is up. That is, the palm-upturned one cannot be inflected, while LIE-DOWN with the base palm down can be inflected. See LIE-DOWN-FRONT for example. I'm referring to the non-dominant hand, not the dominant part of signing.
Do not repeat the movement unless you mean that a person is moving himself up and down. :)
Verb inflection: lie down on the front (classifier).
Verb inflection: lie down on the side (classifier).
Related concepts: LIE-DOWN.
Gloss: MY AUNT IX1 LIE-DOWN READ VORACIOUS++ GOOD[nod]!
English equivalent: My aunt lies down to take in all its great information.