Oversleeping is associated with a variety of different medical problems, including increased weight gain, diabetes, depression, headaches and back pain, according to WebMD. Additionally, those who sleep more than nine hours per night have significantly higher mortality rates than those who average only seven or eight hours.
As of 2015, the correlation between mortality rate and oversleeping has not been determined, as noted by WebMD. However, researchers speculate that depression and lower socioeconomic status, two factors also predicted by oversleeping, contribute to the increase. Additionally, in 2013, a Korean research team studying women undergoing in vitro fertilization found that pregnancy rates were lowest among those who slept between nine and 11 hours a night, according to The Huffington Post.