There is no normal when it comes to mental health. One way to notice an issue is to think about whether you have changed. Do you feel different, or have others commented that you have changed?
Another way to discover a mental health issue is to think about how you view of yourself. If you have been depressed for years, there may not have been a point where you noticed a change, so you have to examine the present. Do you constantly compare your happiness, ability to cope, success, or level of anxiety/worry with others? Do you feel worthless, negative, or disappointed, when compared to the people you know?
If you experience any of the following, seek help:
Lasting changes in your sleep or appetite
Feeling worthless, hopeless, or helpless
Thinking or talking about suicide
Inability to cope with problems or daily activities
Depression that does not subside after a couple of weeks
Extreme mood swings- violent behavior
Strange ideas that seem out of character for you
Strain in your close relationships
We all have some sadness or worry, at least for some of the time. The key is the intensity and frequency of symptoms. Are your symptoms impacting your ability to function at home, work, or socially? Is your issue temporary (such as sadness after a loss or break-up), or has it lasted for a few weeks or months? If your symptoms are severe and lasting, or if you generally feel bad, get help. You can feel better.
Think of psychotherapy as very much like a family doctor: When you are feeling under the weather, you get a check-up and a course of treatment. Whereas doctors often treat the symptoms of the patient, psychotherapists target the root causes of your issues, so that you can work together to solve them, and prevent these problems from taking over your life.