Keep this in mind, your body does more work biophysically while sleeping. Your stress levels decrease, constricted arteries and veins are laxed and swell due to greater flow of plasma, blood, and lymph. The lymphatic system (larger than your entire vascular system) is hardest at work and expands as well to maintain basic homeostasis. Hence, the interstitium becomes greater in size due to many more chemical reactions taking place inside and outside the cells (cell excretion mainly). What do you do every morning after a cup of coffee? Much of that bowel movement was a product of perstalsis within the enterogastric system. Hence, your body gains volume, but tends to "float" or lose weight due to all of this metabolic activity. So all of this energy causes an abundance of interstitium to amass, not only in the feet, but also everywhere in the body through sheer logic., i.e the he puffiness in your eyes that tends to recede during the day.
When we exercise our feet also grow, but no where as large as during an 8 hr cycle of rest.
My advice, get to know your self and do your research, keeping logic in the forefront and the solution should be self evident.
Keep an open mind in an open source