Surah Ad-Duha is a very comforting Surah. It was revealed at a time when the Prophet did not receive the revelation for six months. The Prophet (pbuh) was so worried that Allah did not want him as His prophet any more. Allah (swt) swears by the sun, the amazing light, and by the night.
It is common when suffering from depression that you sleep in the morning and stay awake at night. Allah (swt) is telling us that the days are blessed, and there are better days coming. Allah will reward us abundantly. This is the most beautiful words to say to someone who is feeling sad. Allah reminds us of how He (swt) takes care of our every need, that there is no need to worry. Allah found us lost and guided us.