Too much Fatigue & Sleepiness in Corona.

Its been 15 Days since my brother (age 30) had first time fever on 4th May, On 7th May his rapid antigen test came positive & later he developed dry cough & stomach pain. From 7th to 12th May he took: Vitamin C, Zincovit Syrup, paracetamol, Duolin & budecort Nebuliser. On 13th May I consulted a dr. here in practo & dr. prescribed: Neogadine Elixer Syrup, Gudcef CV 200 Tablet, Predmet 4 Tablet, Calpol Tablet, Limcee Tablet, Zincovit Syrup 200 ml, Lecope M Tablet, IVERMECTOL 12 TABLET. Apart from this he takes Dry Cough Syrup (Dextromethorphan Hydrobromide and Chlorpheniramine Maleate Cough Syrup) 5ml, 3 times a day. Current Oxygen level stays at 92-95% He didn't faced any oxygen or breathing issue yet! Now issue: From 9th or 10th May he is feeling Fatigue & always Sleeping, he stays awake only for 1-2 hrs in a day and wakes for Breakfast, Lunch, dinner tym only, Is it common in Corona or its a serious issue? If its common then how much more days will it take to recover?