583. If I Forgot to Recline, Must I “Do Over”?
Four activities require reclining to the left: 1. Drinking each of the four cups. 2. Eating matzah for motzei matzah. 3. Eating the matzah and marror for koreich. 4. Eating the afikoman.
One who forgot to recline while drinking the second cup of wine must drink it again correctly. If he forgot to recline for any of the other three cups, he does not drink them again. However, with regard to repeating the first cup, if at the start of the Seder he resolved that he might drink extra wine between the first and second cup, he should indeed go ahead and drink it again correctly.
If one forgot to recline while eating matzah for motzei matzah, it is best to be stringent and to eat more matzah, correctly. If he forgot to recline during koreich or afikoman, he does not need to repeat the step.