Wide gap when lying down after breast augmentation. What can be done?

Thank you for your question, and I am sorry that you are having difficulty with your implants.  Without a photograph, or in-person examination, it is difficult to know exactly what is taking place.  It sounds as if the pocket within which your breast implants are sitting is too large.  This can occur either at the time of surgery with over dissection of the pocket, or over time with larger implants as they can stretch the tissues.  I would recommend you see your plastic surgeon for an examination. They will best be able to make treatment recommendations.  

From the description it's possible that the pockets are larger than needed for your breast implants. If over dissected laterally gravity will pull the implant out of position when you're in the recumbent position. This is something your plastic surgeon can discuss with you.