Need help writing a phrase

[nucks2001]

My friend originally wanted to get this phrase translated in some form of japanese (kanji preferably) but it just won't work in that style.

The phrase is "When desire becomes obsession"

I'm looking to write it in classical chinese (or whatever the nicest looking writing is) and because it is for a tattoo.. 4 characters would be ideal.

Thanks!

[iltokyo]

maybe is "心急如焚"

[doraemon]

I know it's a bit late now, but do you guys think 走火入魔 would be an appropriate translation?