רִגְז֗וּ וְֽאַל־תֶּ֫חֱטָ֥אוּ אִמְר֣וּ בִ֭לְבַבְכֶם עַֽל־מִשְׁכַּבְכֶ֗ם וְדֹ֣מּוּ סֶֽלָה׃
ציטערט און איר זאָלט ניט זינדיקן, באַקלערט אין אײַער האַרצן אױף אײַער געלעגער, און װערט אַנטשװיגן. סֶלָה.
Mishneh Torah, Prayer and the Priestly Blessing
He then reads the first section of the Shema and sleeps. If he is overcome by drowsiness, he reads even if it be only one verse [of the Shema] or verses of a supplicatory character and sleeps.
Shulchan Arukh, Orach Chayim
One who is sick [may] pray even lying down on one's side, as long as he is able to concentrate (And if it is not possible from him to pray, nevertheless, one should meditate in one's heart, as it says "Ponder [it] on your bed" [(Psalms 4:5)] (Beit Yosef in the name of Orchot Chaim and Pesikta).