I'm really worried about my mom. She's 64 and had Covid pneumonia back in December 2020. She was on oxygen back then and thankfully recovered. Her breathing seems okay now, but her oxygen levels are always between 94 to 93 when she's awake, and they drop to around 80 to 90 when she's sleeping. We did a chest x-ray two months later, and it showed something called prominent bronchovascular markings of both lung fields. Can you help me understand what that means? Is this something serious or normal? Does she need any treatment for this?