Sleeping on Back After Breast Reduction?

Ideally being on your back and propped up for the first few days helps reduce the swelling and assists in getting up and down. However, there is no recommended sleeping position, basically you sleep in whatever position you are comfortable in and listen to your body.

Great question. The only reason to sleep slightly elevated after breast reduction is to minimize swelling a bit faster. However, if you completely sleep on your back instead of elevated it's not a big deal. Your breasts may remain slightly more swollen when healing for a few days, but otherwise should be able to normalize quickly anyway, whether you sleep on your back flat or slightly elevated. If you are so uncomfortable with your neck pain, then it's not worthwhile to continue sleeping on your pillow.
-Dr. David Mattos, New York Plastic Surgical Group

Hi, understand your frustration as it is uncomfortable to sleep propped up.
I recommend my patients to sleep a bit upright only for 3 days then straight down on their back and after 1 month in any position they like, even on their chest. 

Thank you for your question. We usually ask our patients to sleep propped up for several days following surgery to help decrease swelling in the breasts. I also ask my patients to sleep in a sports bra for the first week after surgery. The bra provides comfort and also helps to minimize swelling due to the compression it provides.If this position is becoming uncomfortable for you, I recommend finding a position that is more comfortable and will allow you to ideally get some sleep. An alternative sleeping position will not cause any problems or ruin your results.Good luck!

I tell my patients after surgery to sleep however they are comfortable with the exception of sleeping on their stomach. If a certain position is painful, your body naturally will not want to do it, and it will likely wake you from sleep and you will naturally reposition yourself. Sleeping in an unnatural position may be worse for your recovery if it's causing pain elsewhere and you're not sleeping well because of that.