Winning in gambling will make your mood happy just as we get some rewards and we feel happy.  These feelings are so great and we feel so energic and positive.
However, once we start to lose in gambling, we slowly move towards the sadness phase. If the loss continues and we keep on losing the money, eventually it can lead to depression.

Yes, I understand that depression is a very severe stage and it won't come at once if you are a new gambler but if you are not a responsible gambler, it is very easy for the gambler to lose his emotions and become depressed in life. Focus on other entertainment other than gambling for some time can be helpful in relaxing our mind and regrouping again to come back strongly in gambling with a strong emotion.