Sleeping with a pillow under your knees is a good thing.
When you sleep on your side, a firm pillow between your knees will prevent your upper leg from pulling your spine out of alignment and reduce stress on your hips and lower back.
Sleeping with a pillow between your knees is also good as it keeps your legs from cramping up and also keeps you more comfortable.
I always sleep with a pillow between my legs and my legs have not cramped up and I get better sleep as well.
It is good to sleep with a pillow between your knees and legs and it's a more comfortable way to sleep.
Not only is it good and comfortable to sleep with a pillow between your knees it's also a good thing because sleeping with a pillow between your knees or legs prevents your upper leg from pulling your spine out of alignment and reduce stress on your hips and lower back.
So if you have back problems or back pain sleeping with the pillow between your knees or between your legs can help prevent that back pain and help relieve any back pain and spine pain.
I sleep with a pillow between my legs and knees every night and when I do it makes it much more comfortable having that pillow between my knees.
Because otherwise my knees will touch each other and make it uncomfortable.
Elevating your legs when you sleep on your back is also good to increase blood circulation too.