Could weightlifting have caused my right implant to fall a bit? 13 year old saline, under muscle implants. (Photo)

If your breast implants were at the same level after 13 years and the right implant dropped suddenly after lifting weights it could be possible that you are implant capsule suffered a tear but I would not expect this with 10-20 pound weights.  I would urge you to see your plastic surgeon for an examination in person to better understand what is occurring. If the right breast implant feels smaller and looser you may have suffered a partial deflation.

Dear miranda707,I understand your concern. However, without a proper assessment it would be difficult to determine what is wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after thorough examination you can get proper recommendations and advice.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

I have seen heavy weight lifting patient develop the look you have but it happens on both sides.  You were only doing light weights (toning) after having had implants for years (capsule well formed) so I would be surprised if your problem occurred from weight lifting 20 lbs.  I would speculate this was happening slowly and finally reached a point where it became obvious to you.  Regardless, you now have an asymmetry and will need a re-do to manage this, preferably with new implants since you're going to the OR anyway.