It is usually not about the hours but the quality and your recovery. Your sleep gets fragmented if you wake up multiple times even briefly. You might sleep 8 hours but if it is broken into chunks you do not get enough deep sleep to feel restored.
Chronic stress keeps your nervous system partially on alert even during sleep so real recovery is blocked. Vitamin deficiencies like iron, vitamin D, B vitamins or magnesium make it hard for your body to convert sleep into usable energy even if you sleep enough.
Blood sugar fluctuations at night from high sugar meals can trigger cortisol and adrenaline waking you subtly. Inconsistent sleep timing ruins your circadian rhythm. Even good sleep will not help if your daily stress is too high. Check with a doctor to rule out sleep apnea, anemia or hormone imbalances.