The Shela Ha’kadosh (a”h) states that one should not lean during the reading of the Hagadah at the Seder. Even though generally one may lean at the Seder even at the points when Halachah does not require leaning, it would be inappropriate to lean while performing the Mitzvah of reading the Hagadah, during which one should sit with a sense of awe and reverence.
Likewise, one should refrain from drinking during the reading of the Hagadah. A person who experiences excessive thirst may drink some water and a person who feels very frail may even drink coffee; otherwise, however, one should refrain from drinking during the reading of the Hagadah, due to the sanctity of the moment, which demands an aura of reverence.
