How common is it? It's extremely common.
Part of the problem is that when you get breast implants, you go to see a plastic surgeon. When you have problems after your surgery, most of the time you're not going to go back to see your plastic surgeon and say, “Hey, I feel sick.” If you have post-surgical problems and complications, of course you're going to go back to the person who did the surgery on you, but when the post-op healing period from the actual surgery is done, you're going to go back to see your GP or whatever specialist would be the one to give attention to your needs.
Most of the time, if you go back to see plastic surgeons, they're going to tell you that it's not your implants. It's anything else. You're going to see specialists. If you tell them, “I think my breast implants are causing this and this”, if it's not a mechanical problem caused by the implants—which most of the time is caused by capsular contraction—they're almost never going to tell you, “I think it may be your breast implants.”