After standing in the hot sun for hours, he began to feel faint and had to sit down.

feel 是动词，意思是"感觉、感受到"。 faint 在这里是形容词，意思是"虚弱的、头晕的"，指因炎热或疲劳导致的不适状态。 feel faint 表示"感到头晕/虚弱"的身体状态。