I'm an insomniac, and let me tell you, disrupted circadian rhythms can do some incredibly destructive things to the body. It can trickle down in so many different and unexpected ways. Memory issues are pretty common. Mental fatigue can make it seem like a person has a different personality at times, because they're just trying to scrape by and don't have the 'energy' to be themselves. Certain parts of the brain may not be recharging and replenishing empty resources.