Hypo? RAI scan?

I may be able to help with some of your questions. Are you receiving a treatment dose (ie 30 to 150mCi's) of radioactive iodine/I-131, or just a scan dose (2-5mCi's)?

If it is a (larger) treatment dose, thyrogen is not yet approved in the US to be used for this except in special circumstances, so 'going hypo', by withdrawal from your hormones and cytomel for the last two weeks is the 'gold standard' for treatment doses.

Even if it is a scan dose, there are some older studies that have indicated that there may be 'false negatives' in some cases with thyrogen; this is mentioned in the blurbs on thyrogen's website as a precaution, so it is often thought to be best to have your first scans by going hypo. Once you have had 'clean' hypo scans in your history, many doctors may be more likely to recommend thyrogen in future.
http://www.thyrogen.com/healthcare/resources/p_hc_res-order_kit.asp

With the 'hypo' symptoms, it is always a 'your mileage may vary' situation, regardless of your current state of health or age. Think positive, though - some folks suffer very few/no symptoms, so hopefully you will be one of these!

The scan itself usually takes about an hour. I found I was quite cold during this - so it is a good idea to dress fairly warmly, as sometimes being hypo can make us colder than normal, too. They will often give us a blanket to cover up with. We lay on a metal table, and the scanner goes over our bodies slowly, while we lay very still.

It is important to remember to remove any kleenexes, etc, from your pockets, as these can be contaminated from your mucous, and give unnecessary 'false positive' readings on the scans - there is info about false positives, and some of the causes of these, here - it also shows you some pictures of what the scans look like:
http://bjr.birjournals.org/cgi/reprint/73/870/627

When we are hypo our bodies often slow to a snail's pace - this includes elimination/bowel movements. It is often recommended that we use a laxative - milk of magnesia works quite well - to make sure to 'get things moving' before the scan. This will often help prevent having to go back another 24-48 hours later to be rescanned, just to check and make sure that any signs in the stomach and/or intestinal tract have 'moved along' as they should.

Has your doctor suggested the low iodine diet? If not, you should consider it anyway - no prescription for this is required, of course, and if it can make a difference in appropriate uptake of the I-131, be it treatment or scan, and give you more successful/accurate results, I think we need to 'just do it'. We normally do this diet for 2 weeks before the scan/treatment dose, and continue it until 24-48 hours after the treatment (or if it is a scan, continue it until you know for sure that you do NOT need to go on to have a treatment dose).

Here is some information:
http://www.thyca.org/ThyCaCookbook.pdf
and here is a cookbook for it that you can purchase, if you like, in addition to the free info in the above link:
http://www.lidcookbook.com/

Some hospitals still suggest we suck on sour candies after taking I-131 - others suggest we now wait 24-48 hours, to protect salivary glands:
http://jnm.snmjournals.org/cgi/content/abstract/46/2/261

Lastly, if you are receiving a treatment dose, you may want to consider the recommended precautions to protect others around you, as outlined in these links; some hospitals are very stringent about these - for example, I was required to stay in hospital in isolation for 48 hours after 100mCi's as a treatment - others are quite lax, depending on your state's radiation regulations:
http://www.cancer.dartmouth.edu/radonc/thyroid/index.shtml
http://www.mythyroid.com/documents/Radioactive iodine treatment UHN.pdf
http://www.thyroid.org/patients/brochures/RadioactiveIRAI.pdf

Hope some of this is useful/helpful for you. All the very best wishes sent your way.