They Are Still Really Nice Standing but Lying Down the Breast Shifts Down and Towards my Underarm. Should I Be Alarmed?

Pictures would be helpful.  Per your description, this not bottoming out.  The outer pocket is a bit larger so the implants migrate that way when you lie down.  This is normal.  If you like the way that the look when standing then I would not mess with the result.

Dr. ES

Based on your description,  you are experiencing lateral breast implant displacement. This is different from “bottoming out”;  this term refers to a breast implant displacement where the breast implant moves too far inferiorly when the woman is standing.

If the breast implant position problem poses a significant concern, capsulorraphy techniques (internal suture repair of the breast implant pockets) may be indicated.   This procedure reduces the size of the implant pocket and prevents the movemnent of the implants to the sides when patients lie down, keeping the breast implants in better position on the chest wall (better "cleavage") and keeping the nipple/areola complexes  better centered on each breast mound.

 I hope this, and the attached link, helps.