While there often appears to be a word that could replace an idiom or a phrase in meaning, this one seems to be an exception (for me that is). I've tried:
- Confused : Less powerful, isn't it?
- Dearth : Needs completion by of something.
- Vacuous : Close, but complete absence of thought isn't the case, I suppose.
- Speechless : Don't know if lack of ideas or happy, shocked etc.
I'm not sure if these words could be ignored because of the reasons I have mentioned, but you can clearly see that I'm at my wits' end on this one!