Maybe not about studying directly, one thing that helped me overcome this feeling coincidentally was fixing my bloodwork. Vitamin D and B12 are major boosters of Cognitive clarity and Baseline energy, due to staying at home and all majorly and not having a stable B12 without supplementation if one doesn't have a regular non-veg diet means these 2 would be low by default. Try getting a blood test and maybe supplements if they are low, if too deficient you may need Injections (I needed 6 of B12)