I suffered from depression for over 11 years.
Until I was diagnosed, I had no clue what the symptoms are.
Even though the symptoms are listed everywhere, to actually read how they affected someone personally may be helpful.
It may seem unnecessary to some, but I didn't realize what was going on with me until I was asked the following questions: Do you have persistent sad, anxious or "empty" feelings?

Yes! I felt the emptiest I had ever felt in my life.
I mean, have very low self-esteem, it was easy to feel empty, But I had never felt anything like the emptiness I experienced.

Do you have feelings of hopelessness and/or pessimism?

Yes! All positive feelings had left me.
Once again, having a very low opinion of myself already, it didn't take much to feel more pessimistic.

Do you have feelings of guilt, worthlessness and/or helplessness?

Yes! I felt guilty about almost everything in my life: family, friends, work.
It seemed as though I had abandoned every aspect of my life, even though, in reality, nothing was really different.

Do you feel irritable or restless?

Yes! I felt very restless because I worried about everything even more.
I became very afraid of "screwing up" at work and doing things like driving.

Do you feel a loss of interest in activities or hobbies once pleasurable, including sex?

Yes! The sex part wasn't an issue because I'm not married.
If I was, nothing would have been happening.
Everything else went out the window.
All I wanted to do was stay in bed.
Literally, stay in bed.
That created more guilt; I wanted to stay in bed so I could dwell on the guilt.

Do you experience fatigue and decreased energy?

Yes! I didn't feel like doing anything.
Everything was a struggle, from taking a shower to going to work.

Do you have difficulty concentrating, remembering details, and making decisions?

Yes! My concentration was completely gone.
My mind was going a million miles an hour on everything related to depression.
Some of the decisions, which I prefer to call choices, I made were awful.
I thought they would make me feel better, but ultimately, they created more stress.

Do you have insomnia, early-morning wakefulness, or excessive sleeping?

Yes! I couldn't sleep at all.
I worried about how the lack of sleep was going to affect everything else in my life, so I created a vicious circle: not sleeping because I dwelled on not sleeping.

Are you overeating or have appetite loss?

Yes! I had total appetite loss.
So much so that I lost 40 pounds over a 3-month period.
I don't know how I kept any strength, but I obviously took in enough nourishment to function every day.

Do you have thoughts of suicide or suicide attempts?

Yes! Suicidal thoughts persisted as my depression dragged on.
I did have a plan in my head, but I never went through with it.
Even though I didn't recognize it at the time, there was a shred of self-worth left in me.
Now, I believe that was God letting me know that He had work for me to do.

Do you have persistent aches or pains, headaches, cramps, or digestive problems that do not ease, even with treatment?

Yes! I developed persistent headaches that were probably caused by the additional stress that I placed on myself.
Because I wasn't eating, my digestive system was a total disaster.

If you know someone who is experiencing any or all of these symptoms, and the symptoms have lasted 2 weeks or more, it would be wise to seek help from a qualified medical professional.
He/she may be suffering from depression.