I think I know how you feel. At least partally. I've been undergoing a CAT scan this morning, too, starting around 4:00 a.m. I haven't had to go to the hospital, though; Wheatley, the CAT in charge here, lives in the same house as I.
I hope you have a better understanding of the reasons behind your CAT scan than I have for mine. I'm guessing yours is diagnostic. Diagnosis seems to be the most frequent purpose for a CAT scan when there is a hospital involved. Some doctor formed some hypothesis about the inner workings of your body and wants to find out whether that hypothesis is true. If that's the case, you can take comfort from knowing that the process is not merely a fishing expedition.
Wheatley, my CAT, is not so much a fisher, either, but he is qualified as a mouser. When he scans me I feel as though he is doing a mousing scan. It is anxiety producing, even though I know that he knows that I am not a mouse. Most likely mousing has nothing to do with it; mousing is probably just the style in which my CAT scans whatever he scans.
At the same time, the CAT is not typically a diagnostician. Diagnosis is not likely the reason for the CAT scanning me. But then what is his purpose? My guess is that this CAT scan is political. My guess is that he is not looking to discover whether I have something such as a bleed in a meninx, but whether I will do something such as turn the outside warm enough that he can profitably go out mousing. If so, the CAT may be disappointed with the findings. (It is December and my sway over the climate is tenuous.)
As I write this, the CAT scan has ended. The CAT himself has retreated into his CAT cave, perhaps to recharge for another round of scanning with perhaps another purpose.