na-adjective
sentimental; emotional; maudlin
Often carries a slightly negative nuance of being overly emotional or self-indulgently sentimental, similar to 'maudlin' or 'mawkish'.
彼の感傷的な話に、思わず涙が出た。
I couldn't help but cry at his sentimental story.
感傷
I became too emotional and couldn't make a calm decision.
センチメンタル is a direct loanword from English 'sentimental' and is often used in similar contexts, but 感傷的 can sound more literary or formal.
Compound of 感傷 (sentiment, pathos) and the adjectival suffix 的 (-tic, -like). 感傷 is itself from 感 (feeling) and 傷 (wound, hurt), suggesting a 'wounded feeling'.