5. Personality differences
If you know someone that might have suddenly gone quieter or not so outgoing whereas they used to be outgoing, it might be a sign of depression. Also, if they’ve become pessimistic but they used to be optimistic, it can also mean they’re suffering from depression.
4. Random mood swings
Someone with a concealed or undiagnosed depression can go through random mood swings. It depends on if their depression is consistent or not. It might seem that these mood swings are happening without cause, but that’s just how depression works. They might have a few bad days followed by a few better days.