Is it ungrateful to feel unhappy as a Muslim?

Feelings are not sins

Many new Muslims hear "just be grateful" and start to feel guilty for every sad moment. But Islam does not judge you for emotions that come uninvited. What matters is what you say and do with them. When the Prophet's ﷺ baby son Ibrahim died, he wept and said: "The eyes shed tears and the heart grieves, but we say only what pleases our Lord" (Sahih al-Bukhari 1303). Grief and faith sat side by side in him. See Did the Prophet ever feel sad?

The prophets complained to Allah

When Prophet Ya'qub lost his son Yusuf, he grieved for years. He didn't hide it; he took it to Allah:

Telling Allah honestly that you are hurting is not ingratitude. It is a form of worship. See What does the Quran say about sadness?

Gratitude and sadness can live together

The Prophet ﷺ said: "How wonderful is the affair of the believer... if something good happens to him he is grateful, and that is good for him; and if something harmful befalls him he is patient, and that is good for him" (Sahih Muslim 2999). Notice that hardship is expected in a believer's life. You can thank Allah for your home, family or faith while still feeling sad about a loss, a lonely season, or a struggle.

Saying "Alhamdulillah" on a hard day isn't pretending everything is fine. It means "praise is still due to Allah, even now." See What does "Alhamdulillah" mean and when do I say it?

What ingratitude actually looks like

• Claiming your blessings came only from yourself, not Allah.
• Using blessings in ways Allah dislikes.
• Constantly complaining about Allah to people, with resentment.
• Belittling what you have by always comparing yourself to others.

Feeling low on a Monday morning is none of these.

When unhappiness doesn't lift

If sadness lasts for weeks, drains your energy, or stops you enjoying anything, it may be depression. That is a health condition, not a lack of gratitude or faith, and it deserves proper care from a doctor. See Is depression a sign of weak faith in Islam?