There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Relationship Between Sleep and Fatigue
- The relationship between sleep patterns and fatigue is complex, with multiple factors influencing the outcome 1.
- Sleep quality, rather than quantitative sleep characteristics, is a significant predictor of fatigue 1, 2.
- Depression and somatization levels are also positively correlated with fatigue, with depression affecting all aspects of fatigue except physical fatigue 1.
Effect of Upright Posture on Fatigue
- Adopting an upright posture may increase positive affect, reduce fatigue, and decrease self-focus in people with mild-to-moderate depression 3.
- Upright shoulder angle is associated with lower negative affect and lower anxiety across both groups 3.
Sleep and Fatigue in Older Adults
- Prior-night sleep is associated with next-day fatigue in older adults, with long and short sleep duration and low sleep quality leading to fatigue 4.
- Time in bed and sleep satisfaction are significant predictors of fatigue in older adults 4.
Distinguishing Sleepiness and Fatigue
- Sleepiness and fatigue are distinct phenomena, with sleepiness characterized by a presumed impairment of the normal arousal mechanism 5.
- Fatigue is a complex phenomenon with multiple conceptualizations and definitions, and its measurement remains subjective 5.
Daily Diary Studies
- Daily diary studies have shown that self-reported nightly sleep quality significantly predicts subsequent daily fatigue ratings 2.
- Total sleep time is a significant predictor of fatigue within, but not between, participants 2.
- Unhelpful sleep beliefs and rumination about fatigue mediate the relationship between insomnia and fatigue reporting 2.