Mondayish
/ˈmʌndeɪɪʃ/ /ˈmʌndɪɪʃ/adjective
Originally of a clergyman: suffering from lethargy or indisposition on Monday, as a result of the work of Sunday (now rare ). Subsequently also more widely: affected by lethargy or disinclination resulting from a busy or eventful weekend, or from having to resume work after the weekend.
Origin
Early 19th century. From Monday + -ish.