Perfect eyelids in morning but they droop and get worse throughout the day. What causes this?

Hi, I've noticed when I wake up in the morning, my eyes are pretty much perfect and are not droopy but throughout the day they start to droop and get worse. This is the case with my brother and mum too, three sisters and dad have perfect eyes. I'm wondering if this could be caused by like a deficiency in something? I can't seem to understand what changes during the day that causes eyelids to droop. Fluid retention? dont think its a heavy eyelid or weak muscle otherwise they'd droop at morning?