Usually signifies the action of unwinding and resting by straightening or spreading out the body. After the hike, she stretched herself out on the grass.
Pro Tip 2/3
Casual Expression
Often used in informal situations to express comfort in one's personal space. He kicked off his shoes and stretched himself out on the sofa.
Pro Tip 3/3
Not Literal Stretch
Doesn't always mean physically stretching muscles; can mean just lying down. Can't wait to get home and just stretch myself out.