I had one of these tests a few months ago and I was propped up in quite a high sitting position. Each hospital might be different though. If you are going to have congestion in your nose or anything that might hinder your breathing I think you should tell the staff. When I had the test my breathing increased quite quickly so you need some clear airways.
I've been told this is an unpleasant test but that it will only be 10 or 15 minutes and over. I planned on talking to them before the test. By the time it's over they'll know from all the snot running down to my chin!
It is a very easy test. They injected some type of dye into me and I layed flat while it took about 15 minute of pictures of my heart at rest. Then I ran on the treadmill for as long as I could and then layed back flat while they took another 10 minutes of pictures. This was the test that finally diagnosed my heart disease. I failed miserably and didn't get to leave the hospital. I had passed a regular stress test and echo
I just had this test on Monday. I have MS and can't run, so they gave me the chemical and I walked on the treatmill (for 2.5 minutes.) Let me warn you, after about 1 minute my heart was pounding and I became nauseaus and dizzie, not fun. It went away shortly after I sat down.
Just had one done today, this is my third chemical stress test. The test is easy..they have changed it from the last time i had one 3 years ago though. I went in today did my time on the treadmill, they put the dye in then i went for 15 min worth of pictures (had a pillow for my head) they checked the pics and said the looked ok and sent me home. If the pics had not looked right they said i would have to leave and come back 3 hours later for a set of pics with my heart rested. Last two times i had the dye put in then had pics, did the treadmill with more dye then more pics. I had a cardiologist in the room with me the whole time i was on the treadmill making sure everything was going ok with my heart. It took about 2.5 hours to be totally done but glad i did not have to go back for more pics and hoping that is a good sign that they liked what they saw Good luck!!