Of course temptation being what it is...and despair being one of the sins against the Holy Spirit....our temptation will always tend towards believing we are separated from God. The thing about conscience is that in order to listen to it with totality--we need to have a perfectly formed conscience.
Our conscience must align with what the Church teaches--and She teaches that one must deliberately place oneself outside of God, in order to commit mortal sin. There aren't any accidental mortal sins. And so to believe oneself to be in mortal sin, through an accident, indicates something other than a properly formed conscience.
It's all about the holy middle ground--we must neither be too harsh, nor too slack upon oursleves. We must make worthy communions, be we must also not keep ourselves unduly from that total physical and spiritual union with our Lord and one another.
You slip up, without thinking, use the Lord's name in vain. YOu ask forgiveness, you accept that the Lord knows your heart and it's intentions, you aren't some legalistic Pharisee, and you entrust your soul to God. Then the next confession- you confess your slip up.
It's a relationship, BA...not a legal contract.