Covid -recovered, diabetic, hypertension

My mother recovered from Covid in July 2021. She has a history of diabetes, pneumonia, hypertension, mini stroke . She is on oxygen therapy only at night . How long should O2 be administered and at what litre? Currently O2 is given from1.30 am to 8.30am at 1 litre. She gets extremely drowsy and sleepy (inspite of good sleep) after breakfast in part because of high blood sugar ( insulin given intermittently when BS reading is above 200) . I want to know what the cause of the sleepiness is ( post-covid ?) , how long will it take to normalise and also if the drowsiness is due to excess of Oxygen ? Also is the light physical exercise she does ithe reason for her BS to shoot up? Would appreciate your feedback. Thank you so much.