Just as lie and lay can get mixed up, there is a confusion with the present participles, laying and lying. The same rules apply as lie and lay, with lying being an action you perform and laying an action you preform on something.
Ed was lying on the floor, kicking his legs in the air like a toddler.
Jeannie was laying the books down, one by one on the table.
I am lying down until this terrible cold goes away.
We took care of Mom, gently laying a blanket over her when she fell asleep.