Ghannouchi, 80, has led opposition to last week's move by President Kais Saied to seize governing powers, dismiss the prime minister and freeze parliament, steps that the Ennahda leader quickly branded a coup.
"After a few hours in the military hospital, Ghannouchi returned home and he is fine now", an advisor said.
Suppressed before the 2011 revolution that introduced democracy, Ennahda has since then been the most consistently powerful political party, backing successive coalition governments and helping to agree the 2014 constitution.
However, economic stagnation, declining services and a public perception of increased corruption have dented its support and Saied's sudden declaration on Sunday appears to have widespread backing.
Ghannouchi, who was also taken to hospital briefly on Saturday and later discharged, faces internal dissent within Ennahda over both his handling of the immediate crisis and his strategic choices since the 2019 election.
Party figures regard the current crisis as the biggest Ennahda has faced since 2011 and a growing number of members have called on Ghannouchi to quit. On Friday he postponed a meeting of the party's powerful Choura council at short notice.