The truth is more nuanced.
Both positions can be comfortable and appropriate for many adults. The better choice depends on your symptoms, health conditions, and personal comfort.
Left-side sleeping
Left-side sleeping may be particularly useful for people with nighttime acid reflux.
Some people also find it comfortable during pregnancy, although pregnancy-specific guidance becomes increasingly important as pregnancy progresses.
Right-side sleeping
Right-side sleeping is a reasonable option for many people who sleep comfortably this way.
Some people may prefer it because of shoulder pain, personal habit, or other comfort considerations.
For people with acid reflux, however, right-side sleeping may aggravate symptoms compared with left-side sleeping.
Do you need to switch sides during the night?
Not necessarily.
If you wake up naturally and want to change positions, there is usually no need to resist the movement.
If you have shoulder or hip pain, alternating sides may help reduce prolonged pressure on one area. However, people with a painful shoulder may need to avoid lying directly on that shoulder.
