I Didn’t Hold Down My Matzah. What now?
Someone who vomited his meal before reciting the after-blessing should not proceed with birchas ha-mazon.
The halachic authorities are divided in their opinions regarding one who vomited the matzah, marror, or the four cups of wine. In practice, he does not need to drink another four cups of wine nor eat marror. He must eat just one kezayis of matzah. (If birchas ha-mazon was already recited, one should wash and recite netilas yada’im before eating the matzah.)