A happy, sorta
olde English way of saying you are
in love, or at least
taken with someone. It is past tense (see above), you are already
had. You are
toast.
If you are smitten, cupid has already made an appearance. Someone who is smitten has that blank stare and goofy smile so indicative of the newly in love.
Many of the characters in the books we had to read in school were thus. It is not likely you have heard this is everyday conversation.
"Yo, homey, you smitten, or what?"