Fluctuating oxygen levels while sleeping

Hello Doctor, My mom's oxygen flucatuates too much during sleep, like it even falls to 65 and then again rises up after few seconds and goes back to normal, and the same pattern follows for most of the resting period at night. When she is not resting, her oxygen level is normal ranging from 94 to 98, but at night, the situation drastically changes. Pulse rate remains normal during sleep, ranging from 57-82( it varies night to night). She was recently diagnosed with covid but she don't feel any shortness of breath or something like that. Also, these days, after recovering from covid, she sleeps too much in 'deep sleep' state and dosen't wake up when her oxygen drops. I am suspecting that she already had sleep apnea but the situation got worse after covid! So, can you please help me out here and let me know what might be the actual cause for it? Thanks and stay safe