Feeling depressed is an emotion that is a state of unhappiness. All people, excluding people who have anti social personality disorder, can experience this feeling. This is not the mental disorder depression rather, this is a basic emotion that is felt by millions a day. On the flip side the mental disorder depression is determines by the DSM-5. This states that if you have 5 of  the certain signs for longer than 2 weeks CONSTANTLY, you have depression. The signs are as followed, Constant depressed mood, lost pleasure in most or all activities, significant weight gain or loss due to loss or gain in appitite, slow down of thought or physical movements, fautige or loss of energy, feelings of guilt or worthlessness, diminished ability to think or concentrate / indecisiveness, recurring thought of death or suicide. If you noticed constant depressive mood is only 1 of 8 of the signs of depression. You dont technical need to feel or experience the emotion of depression to have the mental disorder of depression. Please stop self diagnosing yourself with depression because you were sad and tired on the same day


Edit: Changed some wording around