I'm sorry to hear of your difficulties. Leaking would be easily diagnosed by gradual decrease in breast size, increased rippling, and eventual deflation. Pain would not usually be associated with a saline implant leak or deflation, and the saline inside your implants is identical to intravenous saline and is harmlessly absorbed.
Bottoming out occurs when the scar capsule around your implant is so thin and pliable that your breast pocket opens up (scar capsule stretches or tears through) in an undesired direction--in this case, inferiorly. Sometimes the pocket can open up laterally or in the armpit, allowing sideways implant displacement. When too-tight push-up bras (or overly-dissected pockets centrally) stretch the cleavage tissues from the breastbone, symmastia ("uniboob") occurs. Inferior pocket stretch or downward implant malposition is called "bottoming out" and requires suturing the internal capsule (capsulorrhaphy) to tighten and close off the pocket and raise the implant back into normal position.
But bottoming out usually does not cause pain, unless a small skin sensory nerve is being stretched by the dropped implant's pressure. (Possible, but truly unusual.)
Bottoming out is visible by looking at your implant position in the mirror. If its position has been good for 10 years, it is unlikely to have "suddenly" dropped too low. Perhaps it's been moving that way gradually, and now your occasional pain becoming two months of more severe awareness has drawn your attention to it.
Without exam or photograph it is impossible for any of us online to tell, but even you can make the diagnosis of deflation or malposition. If you think there's a concern, go see your plastic surgeon, or find another ABPS-certified plastic surgeon for a quick exam. If you are simply worried about your 10-year-old implants, there is really no need to be concerned unless you do indeed have leakage or malposition. SImple implant replacement or pocket repair can solve these issues with an easy re-operation.
Pain can also sometimes be part of capsular contracture, which can be late and unilateral, and starts out as pain and/or firmness. This may be more subtle at first, but your plastic surgeon will be able to determine if this is an issue.
If you need or want new implants, I would suggest the newest generation of cohesive silicone gel implants (by any of the three FDA-approved implant manufacturers). They do not "leak," and I believe they most emphatically do NOT require MRI scans every 2-3 years to look for "silent rupture." But they are softer, have less rippling, feel more natural, and can never deflate. (And you can change size too, if you wish.)
Go see your PS or a new one and relieve your concerns! Best wishes!