Smitten \SMIT-n\ , adjective;
1. Struck, as with a hard blow
2. Grievously or disastrously stricken or afflicted
3. Very much in love
I had an 'aha' moment about this word recently. I've only heard it in the context of "very much in love," but I noticed how orthographically similar it is to that good old Biblical word smite. Turns out, there's a good reason for that: they're the same word.
Smitten is first attested in the mid-13th century as the past participle of smite. Smite comes from Old English smitan ("to hit, strike, beat"), which had a past participle smiten. It derives from Proto-Germanic *smitanan, which possibly comes from Proto-Indo-European *(s)mei- ("to smear, to rub").
This idea of being "very much in love" appears in the 1660's. I guess they decided that to fall in love was a very grievous infliction indeed.