I remember when I got my wisdoms out, I got the Versed/fentanyl combo as well and there was indeed no high/rush.
As someone mentioned already, lack of rush/euphoria from hospital-administered IV meds is really common, unless you have low/no tolerance to an opioid and the doctor is generous with the dose. Usually in the dentist's office or hospital, they only give just enough medication to treat the acute issue. Like one time I was in the ER and my pulse was well over 125 steady and the doc could've easily ordered a 4mg lorazepam shot and resolved the issue, but he'd also likely have put me to sleep for a while too lol.
Benzos are notorious for not having a rush or IV advantage, except a select few, midazolam/Versed being one of them. But again, you'd maybe need an injection of 15mg to achieve this, but typical adults are usually given ~5mg for an average procedure.
The same goes with opioids/painkillers. In fact, when opioid naïve individuals come to the ER for example with a rather painful injury, too high of a dose of an opioid often makes them sick (to their stomach, or to the point of throwing up, just as a lot of people puke their guts out when they start taking potent opiates recreationally.
I had an ATV accident once while on vacation that resulted in a gash on my forehead requiring 33 stitches, it hurt like hell because it was a head injury and I'd classify it as a "rather painful injury." Well, I was pretty opioid naïve at the time and as soon as they got me on the table and an IV line in, the nurse gave me 2mg of Dilaudid along with Zofran to prevent any nausea. I felt nothing from the Dilaudid. I was still in too much pain, so she gave a second 2mg shot probably about 10-15 mins later. Again, I felt no rush or high, but finally my pain was relieved enough that I could relax for a while. A 10mg hydrocodone pill gave a clearly noticeable (mild) rush along with some euphoria at that time in my life, yet somehow a much stronger med like hydromorphone IV did nothing.
I've read and am convinced that when you're truly in a good amount of pain, a dose of a med like morphine 10mg may simply have only analgesic effects even if, when not in pain, the same dose would provide a good buzz for you.
This is a stupidly post, but you get my point. I'm not stating this all as fact for every human, but I'll say I've heard of these scenarios several times. At the end of the day, sure there can be more to IV use if you choose to pursue the "more," and there are soooo many different IV meds/drugs and experiences that go along with them, but that's a path proven by many that leads only to a downward momentum and is not worth it. I agree with the others in explicitly advising against it.
In FACT, you're totally right. IV is none better than oral, smoking, or snorting. Don't get me wrong: I don't encourage usage via those routes either, but IV isn't worth exploring for any reason at all, and I can guarantee that your life will remain substantially better by not even considering it any more. Stick with where you're at currently.
Very Sorry for the long post!