They normally do the Dix-Hallpike test first anyway, which will immediately tell them if it really is BPPV. If it isn't, they won't proceed to the Epley, as it wouldn't make any difference one way or the other.
You can look up the Dix-Hallpike on-line and try it on yourself right now. You can't do yourself any harm with it. And you don't need to hang your head over the end of the bed like it says, just throw yourself down fairly quickly. You'll see what I'm talking about if you look it up.
If the Epley is done by an incompetent operator, there is a small risk the crystals can get into the lateral canal, which can make you feel very bad. However, this doesn't last. It sorts itself out overnight. Having researched this, I'm convinced that this is what happened to me when an ENT doctor attempted the Epley on me for BPPV about 25 years ago. I did indeed feel dreadful in the immediate aftermath, but I was back to BPPV "normal" (i.e. vertigo when I moved my head into certain positions, and general unsteadiness) by the following morning. The BPPV eventually cleared itself up after about a year.
I got a second attack of BPPV (in the other ear) at the beginning of this year. This time I saw a specialised vestibular physiotherapist, who performed the Epley and completely cured me in one 20-minute session, which included the initial assessment. Just like that! That was 3 months ago and I haven't had the slightest problem ever since.
On researching the history of the Epley manoeuvre, I was surprised to find that it was only invented in 1978 (Dr. Epley is still alive today) and didn't come into general use until the early 1990s, which is when my first manoeuvre was performed. I now suspect that there wasn't enough knowledge about how to do it among practitioners in those early days, so the doctor didn't complete the manoeuvre correctly, allowing the crystals to wander temporarily into an even worse position.
I think there's very little chance of that happening these days, when the Epley is a well-practised everyday manoeuvre. Most of the cases where it has happened recently seem to be where people have tried to perform the Epley on themselves. You really should never attempt that.
When it's done by a competent modern operator - and where the diagnosis really is BPPV - it's a very easy procedure that just takes a few minutes. They have to induce vertigo at two different points in the procedure, just to verify that it's working, but it's no worse than the vertigo a BPPV sufferer experiences when first lying down, getting up or turning over in bed. And trust me - it's well worth it for the instant relief!
If you're still nervous, you can find some good YouTube videos showing how it works.
Do come back here and tell us how it went, won't you. After my most recently Epley I was so overjoyed with the results, I was all over these boards like a rash within minutes of getting home!