Write down your sins on a paper, so you won’t forget them.
But you must also know this: that if you do not consider your sins properly before you confess them, whatever sins you forget and do not confess, are unforgivable, because the forgetfulness was done by you deliberately, because you could have remembered them by considering them and did not do so.
But if you consider them properly and forget some sins of yours, being a unmindful man, as you are, that sin, it is said by some, is forgiven along with the others which you have confessed, because this forgetfulness is not deliberate, but unintentional.
But if you remember a sin of yours after confession, you must go again to the Confessor and confess that too.
St. Nicodemus the Athonite