Their personality changes.  

You may notice sudden or gradual changes in the way that someone typically behaves. He or she may behave in ways that don’t seem to fit the person’s values, or the person may just seem different.

They seem uncharacteristically angry, anxious, agitated, or moody. 

You may notice the person has more frequent problems controlling his or her temper and seems irritable or unable to calm down. People in more extreme situations of this kind may be unable to sleep or may explode in anger at a minor problem.

They withdraw or isolate themselves from other people. 

Someone who used to be socially engaged may pull away from family and friends and stop taking part in activities he or she use to enjoy. In more severe cases the person may start failing to make it to work or school. Not to be confused with the behavior of someone who is more introverted, this sign is marked by a change in someone’s typical sociability.

They stop taking care of themselves and may engage in risky behavior. 

You may notice a change in the person’s level of personal care or an act of poor judgment on his or her part. For instance, someone may let his or her personal hygiene deteriorate, or the person may start abusing alcohol or illicit substances or engaging in other self-destructive behavior that may alienate loved ones.

Have you noticed someone who used to optimistic and now can’t find anything to be hopeful about? That person may be suffering from extreme or prolonged grief or feelings of worthlessness or guilt. People in this situation may say that the world would be better off without them, suggesting suicidal thinking.