I think that that are two kinds of "confession" and "penance" in the Church, each corresponding to the relative gravity of the sin(s).
In the case of relatively minor shortcomings/sins, the communicant is not so alienated from the Lord and His Body that he must formally confess to the Lord in the presence of His priest. Thus, the normal cycle of services, prayers/fasting culminate in the Divine Liturgy's prayers before communion. Keep in mind, that one is always confessing and asking for Divine mercy. The Trisagion prayers that we constantly say contain such prayers: "O heavenly King, O Comforter, the Spirit of truth, who art in all places and fillest all things; Treasury of good things and Giver of life: Come and dwell in us and cleanse us from every stain, and save our souls, O gracious Lord...All-holy Trinity, have mercy on us. Lord, cleanse us from our sins. Master, pardon our iniquities. Holy God, visit and heal our infirmities for thy Name's sake...Our Father, who art in heaven, hallowed be thy Name; thy kingdom come; thy will be done on earth, as it is in heaven. Give us this day our daily bread; and forgive us our trespasses, as we forgive those who trespass against us; and lead us not into temptation, but deliver us from evil." Not satisfied with just the Trisagion, such prayers abound and culminate in the DL pre-communion prayers: "I believe, O Lord, and I confess..." and "Of thy Mystical Supper, O Son of God.." Nonetheless, most Priests do insist that a communicant go to private confession in regular intervals to make sure that the communicant is in the right path.
In the case of serious shortcomings/sins or by a voluntary non-participation in Holy Communion, the communicant is indeed alienated from and must be reconciled to the Body. In this situation, one must confess to the Lord in the presence of the Priest. Spiritual guidance, penance in some instances, and formal absolution would follow. And, if the communicant gets mad at a tailgating driver on the way to the DL next morning and lets fly an obscenity, I do not believe that many priests would think that this shortcoming would make the communicant unable to receive the Holy Cup that day, if he is truly sorry and is determined to curb his temper and his tongue. Indeed, a self-imposed abstinence from the Cup may be an indicator of a much greater sin--that of spiritual pride, which is of the serious kind of shortcoming.