The sign of having done a good deed is feeling close to God. Feeling far, estranged from God is the sign of having done something wrong.
The 11th of the 13 Principles of Faith outlined by Maimonides is faith in reward and punishment. There is the reward and punishment of the future, in the World to Come, but there is also immediate reward and punishment, in this world.
There is no better feeling than feeling close to the Almighty, and no worse feeling than feeling far and estranged from Him.
If a person does a mitzvah (a commandment of the Torah, a well-defined good deed) and still feels far from God (the Commander of the mitzvah) it must be that either he did the mitzvah by rote or that some egocentric motive entered his consciousness while performing the mitzvah. Performing a mitzvah for its own sake, to fulfill God's will and one's mission in life, will always bring with it a sense of closeness to God.
Sometimes one experiences a momentary high after performing a mitzvah and subsequently experiences a fall of spirit. The Ba'al Shem Tov explains that this is because the high was no more than a sense of self-satisfaction, not one of true joy in having merited to do good, in service of God. The sense of self-gratification that comes almost automatically with the performance of a mitvah is likened to the venom of a snake that bites the heel of man, symbolizing the end of a deed.
So don't confuse between the false, impure sense of self-gratification and the true, pure sense of feeling close to God.
