expression, godan verb (-mu)
full stomach, sleepy head; when the belly is full, the eyelids droop
A proverb meaning that after eating one's fill, one naturally becomes sleepy. The literal image is that when the skin of the belly is stretched tight, the skin of the eyelids sags.
腹の皮が突っ張れば目の皮がたるむというから、食後はどうしても眠くなる。
As the saying goes, 'full stomach, sleepy head,' so I can't help getting drowsy after a meal.