I thought I'd have something to contribute to this thread, but it looks like people have already hit all of my fantasy high-points.
I dream about being taken back to an exam room where I am told to strip down to nothing. The nurse doesn't leave while I strip off. He or she stands there and asks me some general medical questions. Once I'm naked they say "Ok, let's get your height and weight" and lead me out of the room down a busy hallway to a scale up front by the nurses station. I have to stand there nude and wait for a bit while the (female, nude) patient in front of me gets weighed then turns around to get her height measured and sees me there just as naked. She tries to cover herself and is asked to stand straight with her hands at her sides. I start to get hard as she is led back to her exam room. After my weight is taken and I turn around for my height, I see a quick flash and realize that I have been photographed standing against a grid on the wall to record my height. As I'm led back to my exam room I wonder what will happen to the pictures.
Sometimes I like to imagine that the patients are given embarrassingly small covers to wear for "modesty" especially if they might be seen by people in the waiting room.
For men it would either be something like a front-only loin-cloth that is barely long enough to hide the genitals and is made out of the same flimsy paper as disposable gowns, or else it is an extremely stretchy but extremely small thong-style sling-type brief, also with no real back. Neither of these garments provide any coverage if you get even the hint of an erection. The paper loin cloth has nothing holding it down so the penis simply pushes it out of the way, and the thong is fairly translucent to start with and just stretches with the erection. Both have the added indignity of very clearly showing any wet spots.
For women patients the bottoms would be the same two options, and they would have matching options for tops. The loin-cloth would have a similar bra-style top that looks a lot like a drip-cape from a dentists office, but it is split in half, one side for each breast. It has a non-adjustable neck string, and an elastic tie around the bottom. The bottom tie runs through a fold along the bottom of the two "curtains" so they can inconveniently slide around. The nurse are generally no good at picking the right size for patients breasts so women are always either bursting out or the tops are too loose to hide anything. The g-string bottoms have a bra-style top that has two shoulder loops and two tit-bags" made of the same super-stretch material as the bottoms. Women with anything but the smallest breasts have to lean forward to slip their boobs into the sleeves, then pull the straps around each shoulder. They stretchy tops only come in two sizes and do nothing to hide the patients nakedness. If anything they highlight it by drawing attention to their chests. Male patients obviously have no need of an exam top.