My father said the same for me. To this day, sleeping in the car is the easiest sleep i get. It's so soothing. Which is problematic considering i'm the sole driver for my household hah.
Many car seats are removable and have carry handles so it is possible to hang them and have them moving like a pendulum also spinning. For safety use a strong strap (like for a hammock) and hang just an inch or few cm or so above the ground and make sure what it is hanging from can not topple or come crashing down.
