Hitting your sleep sweet spot can be a shot in the dark most nights, no pun intended. This could be due to a phenomenon known as "sleep debt," according to the National Sleep Foundation, which finds us sleeping, say, 5 hours one night and then trying to make it up by sleeping 9 hours the next night. Another factor could be that you're not sleeping the right amount for your age. While ages 18-65 all require 7-9 hours of sleep a night, there are new recommendations for younger and older aged people. As it happens, you might be OK on the lower end of the scale, as a 2013 study in the Frontiers of Neuroscience as well as one in the Sleep Science journal found that more than seven hours did not increase cognitive function or raise mortality rates. How many hours of sleep do you need? How many do you actually get? Comment below.