I thought these quotes which I came across in, "Letters from the Desert" by Sts Barsanuphius and John may be of some help:
...If a fantasy occurs to me by night and, on the next day, there is Holy Communion, what should I do?
Response by John
Let us approach with all our wounds and not with any contempt, as people who are needful of a doctor, and he who healed the woman with the issue of blood (Mt 9:22) will also heal us. Let us love much, tha He may also say to us: "Your many sins are forgiven; for you have loved much" (Lk 7:47). When you are about to take Communion, say: "Master, do not allow these holy things to be unto my condemnation but unto purification of soul and body and spirit." Then, you may approach with fear, and our Master, who is loving-kind, will work His mercy with us. Amen.
A Christ-loving layperson asked the same Old Manif one should reflect a great deal about the sacred mysteries, and whether a sinful person approaching these would be condemned as being unworthy.
Response by John
When you enter the holies, pay attention and have no doubt that you are about to receive the Body and Blood of Christ; indeed, this is the truth. As for how this is the case, do not reflect on it too much. According to him who said: "Take, eat; for this is my body and blood" (Mt 26:26-28), these were given to us for the forgiveness of our sins. One who believes this, we hope, will not be condemned.
Therefore, do not prevent yourself from approaching by judging yourself as being a sinner. Believe, rather, that a sinner who approaches the Savior is rendered worthy of the forgiveness of sins, in the manner that we encounter in Scripture those who approach him and hear the divine voice: "Your many sins are forgiven" (Lk 7:47-48). Had that person been worthy of approaching him, he would not have had any sins. Yet, because he was a sinful man and a debtor, he received the forgiveness of his debts.
Again, listen to the words of the Lord: "I did not come to save the righteous, but sinners" (Mt 9:13). And again: "Those who are well have no need of a physician, but only those who are sick" (Lk 5:31). So regard yourself as being sinful and unwell, and approach him who alone can save the lost (cf Lk 19:10).