Could it mean a troubled child? When I read your post, I thought of that possibility. Also a lifelessness in a person or just behing dehydrated. As a timing card it could literally mean sunset.
Thanks for dredging this oldie up
And yes, the Sun relates to children, both literally and figuratively--youthfulness, play, feeling that strong, clear energy--or literally a child or children. However, I wouldn't immediately see the Sun that way unless there were other cards in the reading confirming it (like pages), or if the question was some parent asking about their kid or family.
And in that instance, I would't see lifelessness in the Sun rx; the Sun rx reminds us of Phaethon, son of Helios (Sun god), who took his dad's fiery chariot for a spin, and was so unable to control it, and so in danger of burning up the Earth, that Zeus had to bring him down with a thunderbolt.
Thus, the Sun rx (to me) would not suggest the opposite (a lifeless child or person--as I think there are other, better cards to suggest that), but rather one who couldn't control or channel that sunny energy. Who was burning and destroying with it rather than energizing with it--maybe ADHD?