The nausea and feeling faint can be caused by lots of other reasons as well...I would look into that especially if you've never experienced them before with going off of this med.
Going off Synthroid for two weeks is not going to make you feel that bad. Thyroid medication has a half life of one week, so in two weeks you still have one week of thyroid med in you. I notice you are female, is it likely you could be pregnant? I don't see your age on your profile.
It could also be a virus you have and not related to the going off the synthroid.
I know in some areas Thyrogen is not available, is that why your doctor is not doing it that way? Or is it that your doctor is unaware of Thyrogen?
WBS = whole body scan (I-131)