וַיְמַהֵ֣ר שָׁא֗וּל וַיִּפֹּ֤ל מְלֹא־קֽוֹמָתוֹ֙ אַ֔רְצָה וַיִּרָ֥א מְאֹ֖ד מִדִּבְרֵ֣י שְׁמוּאֵ֑ל גַּם־כֹּ֙חַ֙ לֹא־הָ֣יָה ב֔וֹ כִּ֣י לֹ֤א אָכַל֙ לֶ֔חֶם כָּל־הַיּ֖וֹם וְכָל־הַלָּֽיְלָה׃
Then Saul fell straightway his full length upon the earth, and was sore afraid, because of the words of Samuel; and there was no strength in him; for he had eaten no bread all the day, nor all the night.
Read midrashic interpretation of I Samuel 28:20: and classical rabbinic exegesis.