If I forgot to confess a mortal sin, was it forgiven?
I recently went to confession, received absolution, and did my penance. Subsequently I remembered something I did years ago that I never confessed. Am I absolved of that one as well? If the sin was mortal, does that need to be addressed specifically?
So long as you intended to confess all your mortal sins and otherwise make a good confession, then the sacrament was valid, and you were forgiven all your mortal sins. The fact that afterward you remembered another one does not mean that you are in a state of mortal sin.
The Code of Canon Law states, "A member of the Christian faithful is obliged to confess in kind and in number all grave sins committed after baptism and not yet directly remitted through the keys of the Church nor acknowledged in individual confession, of which one is conscious after diligent examination of conscience" (CIC 988:1). Since you remembered this grave sin, you should mention it in your next confession.