Fantasizing ok or not ok?

I love my husband we have been together for 19 years we got married young, but sometimes I fantasize that I have sex with other men to get horny, I don't n won't cheat on my hubby but is it normal? It does help me be more hot n passionate during sex does anyone else feel like that too? My heart still jumps when I see my hubby I love him so much but am I just dis functional? Sometimes I even feel guilty without doing anything wrong.