The thought I'd like to share was said during the holocaust by the Piazeczna Rebbe hy'd who uplifted others amidst the depressing conditions of the Warsaw ghetto. It is written in the Sefer Aish Kodesh, which was compiled from the notes that he hid before he perished.
The Tikunei Zohar teaches that Purim is similar to Yom Hakipurim. The Piazeczna explained this parallelism in the following manner. The essence of Yom Kippur, just experiencing the day, can accomplish Teshuva even for those unable to achieve a full Teshuva on their own (Rambam Teshuva 1:3). Similarly, a jew who is depressed and unable to achieve full simcha should nevertheless put in hishtadlus and the essence of Purim will accomplish this Simcha for him. The very day of Purim thus accomplishes simcha for all! May we all merit this "antidepressant" gift.
A freilichen Purim!