The position you sleep in after breast augmentation does make a difference. Each plastic surgeon may have a slightly different protocol or rules, but the general principle is that gravity can help us control the swelling after surgery and pressure in the wrong place can perpetuate swelling or shift position of implants that may be difficult to correct.
We recommend sleeping on your back and a little elevated (like in a recliner chair) for the first 3 weeks after surgery. Gravity in this situation pulls the swelling downward and away from the implants. If you sleep flat then the excess fluid does not drain and the swelling will persist. This may not affect your final result, but makes the healing process slower and more uncomfortable for longer. If you sleep on your sides, the side that is down may swell significantly and result in popped stitches, delayed healing and asymmetric results with implant shifting…. All situations that could be avoided.
Realize that eventually you can go back to your normal sleep routine safely and comfortably, but adhering to the rules and following your doctors recommendations during the important early healing time will simplify and speed the journey to that point.