Pierre,

I prescribe Nystatin quite frequently to my patients and have never had one complain of Nausea. I checked Medline Plus and Nausea is not listed int he side affects for Nystatin. This doesn't mean it can't be one. The link is below.
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682758.html

I would get your blood pressure checked and get some blood work done if it were me just to rule out other causes. Tell you doctors.

I hope this helps.

Cheers,

Mike