U must be lyn - that can't be true!
|NGL||Not gonna lie|
|Planking||Lying face down and straight like a plank|
|LOTFLOL||Lying on the floor laughing out loud|
|TOD||Truth or dare|
|TTTT||Too tired to talk|
If someone accuses you of lyn, they think you are not telling the truth. However, if someone says they are lyn down, it means they are "laying down" - likely on a bed, floor, couch, or other flat surface.
It is, of course, possible to be both lyn and lyn down. This can lead to sticky situations in which you must accuse someone of telling mistruths while they are laying down - in which case you should likely just call the person instead of sending a written message that includes this abbreviation.