Hey,
What kind of shunt did you have put in may i ask?
Fixed pressure (High medium low)
Or an adjustable programmable one?

Reason I ask is that I currently have a fixed pressure one, I went into hospital the other week, feeling headachy (not bad headaches, just little ones) and Nauseous, which had continued for weeks...its now been about a month ongoing.
Well, I was given ICP monitoring over a period of 2 days, which suggested that I was overdraining, meaning the shunt was working too well and was taking too much fluid away from my head.
Therefore Im going into hospital tomorrow to be admitted again and have my shunt changed to a programmable to try and control this problem.

I wasnt aware that headache and nausea was a symptom of overdraining otherwise things would have clicked alot sooner than they did.

I do just hope, its your head adjusting from high pressure to a relatively normal pressure though. But of course, as anyone would say, if your concerned do just ask your neurosurgeon for his prospective of what is causing the nausea, should it be related to whats happening inside your head.
Good luck!!