Should I Wear a Sleep Bra at Night to Keep Breast Implants in Position?

I recommend you wear a bra for the first eight weeks of recovery, day and night, to minimize the risk of displacement. However, you should really ask your surgeon, as they may have different guidelinesBy now, most likely your implants have settled and yous hold be okay to sleep in whatever position you'd like. 

The #bra acts as a “dressing,” holding the breasts in
position. If the bra feels too tight or hurts, switch immediately to sports
type bra that feels comfortable. You should wear the bra at all times for at
least three weeks. You will probably be more comfortable if you do not wear an
underwire bra. You should always use support. It is always recommended to call and see your surgeon to discuss your concerns.

At 4 months post surgery, wearing a bra to bed, in my opinion, will have little effect on implant positioning.  Sleeping on your back for the first 2 weeks is a great idea to decrease implant malpositioning.  I do not have my patients wear a bra for the first month after surgery, and only an ace wrap to keep the implants from riding up.  Side to side malpositioning has never been an issue in my practice.