I've had some pretty good luck other than two incidences. One of them was just a very young nurse that has serious issues sticking a needle in my vein to draw some blood. It's the only time needles have made my physically ill. I had to beg her to stop trying. My veins roll and are very small, they apparently aren't all that easy to get into.
An other time, I was going in foe some exploratory stuffs, and they put one of those starter needles in so they could inject some stuff into me later. I laid there for an hour and a half before they got me in to where they would actually inject me with something. I informed the nurse that I though the needle may have come out of my vein. I wasn't sure, but it sure felt wrong. She told me to stop whining. Anyone who knows me knows that physical pain does not cause me to whine. Well she proceeded to shoot a pile of Demerol into my muscle, and it burned like crap. I calmly said to her that I didn't think it went into my vein because it was burning rather bad. She said to me "You are such a whiner!". Well after 3 seconds of me not passing out, I informed them I was still extremely conscious, and please don't stick the camera up my ass just yet. Then I rolled around and looked at the doctor and asked him to please try again. He stuck me in the hand and got a good shot of Demerol in me The last thing I said before I went under is "oh, yeah, now that feels real nice, just how its....." Now I always ask for someone who has some experience to stick me in the vein, and warn them that I roll.
I think one of the issues is that the nurses get a lot of people in there that just like to complain, or don't have a high threshold for pain. When you are actually feeling something serious, you need to make sure they know that you aren't just complaining., and ask them to do the tests you think they should do. I haven't been in hospitals too much to know the general atmosphere, but when your every dy is wrought with aches, pains, and far more serious situations, I think you just get desensitized to the way people react to their pains.