An incredibly rare medical condition has been blamed for a woman's mystery abdominal pain that disappeared every time she lay down.
The 28-year-old Michigan woman told doctors whenever she stood up, it felt like a "ball" was "rolling inside" her, according to a report in journal BMJ Case Reports.
She'd experienced the bizarre sensation for six years, and had seen "several" doctors without luck.
Specialists at the Vattikuti Urology Institute at the Henry Ford Hospital in Detroit did a scan of her pelvis, and noticed her right kidney was in totally the wrong place - about 6cm too low.
Symptomatic nephroptosis, or 'floating kidney', is rare and no one really knows what causes it. It does appear more often in women with low body fat however, and it's believed the kidney simply falls down because there isn't enough fat to hold it in place.
Pain happens when it kinks the duct between the kidney and the bladder, causing urine to build up and swell the kidney like a balloon.
Strangely, pregnancy eased the symptoms - the growing uterus pushing the kidney back into its right place.
Prior scans had failed to diagnose the problem because they're usually done lying down, showing the kidney in its usual spot.
A robot was used to perform a laparoscopic nephropexy - literally tying the kidney to the back wall of her body. This fixed the problem instantly.
"The patient was grateful that her symptoms had finally abated after six years," doctors said.
Despite the rarity of the diagnosis, it's estimated up to 20 percent of women experience minor nephroptosis but don't show any symptoms, so it's not a problem.