This can vary by person. Some people settle for 6 hours of sleep, while others will need 9 full hours. In reality, the goal is simply to get up feeling rested. So this can be a way to calculate how many hours you need each night.
Not only does fatigue appear to be linked to sleep and quality of sleep, but stress is also present. In particular stress can make us need more sleep. On the other hand, stress can also affect the quality of sleep, which means that we enter into a kind of vicious circle in which our daily performance is affected. Memory problems, concentration problems, crying crisis, and other issues can all be consequences of fatigue.