Why is my female guppy lying in the substrate?

Lately my female guppy has been lying down in the gravel in one particular. I don't see any particular signs of any diseases or fungi. I know it's not pregnancy because she gave birth a week ago.


In the photo it looks like she's hovering but earlier she was sitting

AMMONIA: 0ish - yellow but a slight green tint- likely due to high sensitivity to tiny amounts of ammonia
NITRITE: 0
NITRATE: 0ish
PH: 7.4ish

my female platy has been doing that the last 8 months and she still comes up to eat. she also had given birth 4 times in that and all her babies have been very healthy. it’s very confusing. maybe some sort of live bearer thing if they get old?