Awww, you never know, if it's a consultant who does this all the time, maybe they may have a less painful way of doing things.
I've not had my heels done but had injections deep into both hips and shoulders. It wasn't a quick process either time (both had staff training/observing) though interesting to listen too. They used a numbing spray and I think put some anaesthetic in with the injection too. I do have quite a high pain threshold but all of them were fine.
I was bracing myself with my first hip one, especially when my consultant said I could shout, scream, swear, just not move! Both hip ones were fine, they even went right in down to the bone (and I have not so insignificant hips!).
Might be an idea to have a back up plan in case you are advised not to walk on them afterwards. I didn't realise with my hips until they said that due to the anaesthetic did I have anyone to take me home. Errrrr, no! I was wheelchaired to the taxi phone.
I thought my shoulders were going to be really painful after hearing my mum's tales of the ones she had. Hardly felt them.
Hope it goes well tomorrow x